Bad Catalytic Converter Rattle? 5 Ways to Fix This Sound

When your car has seen thousands of miles, it’s not uncommon for you to experience a bad catalytic converter sound. That means the catalytic converter is coming to the end of its lifespan and you will experience a catalytic converter rattle along with other symptoms, such as performance reduction and the “check engine” light coming on. 

Replacing a bad catalytic converter can be quite expensive, so today we will not only discuss the different causes for a catalytic converter rattle, but we will also discuss the ways you can fix the noise or reduce it before you can get your car to a mechanic. 

Once you notice a catalytic converter rattle, there are many different ways to stop the noise or control it before there’s no other option but to replace the part. Today, we will provide many different fixes and you will be able to perform them at home with some basic tools and very little expense. Without further ado, let’s get started with this complete guide on how to eliminate catalytic converter noise. 

What Is a Catalytic Converter?

Before we discuss the different kinds of catalytic converter noise and the causes for a bad catalytic converter, we want to talk a little bit about what it is and what it does for your car. 

As you know, engines use an internal fuel combustion process to produce power, which is why they need an exhaust system and the catalytic converter is part of that system. It uses catalysts to produce a chemical reaction that cancels the pollutants created by the fuel combustion process, which are terrible for the environment. 

Catalytic Converter neat labeled diagram of it's parts and how it works
Image Source

Most commonly known as a “cat”, it consists of three main parts; the heat shield, which surrounds the catalytic converter to keep high temperatures from escaping. The shell or casing, which is the main body where the internal components produce the chemical reactions mentioned above. And the high flow honeycomb catalyst, which is inside the cat and it allows the exhaust to go through. 

When the exhaust enters the cat, it will go through the honeycomb and come in touch with the catalysts, which will produce the chemical reaction necessary to cancel the pollutants. Now, there are two types of catalytic converters that control the chemical reaction; reduction catalysts and oxidation catalysts. 

They are both necessary because hydrocarbons and carbon monoxide require a lean combination of fuel and air to convert properly. At the same time, nitrogen oxide requires a rich combination of fuel and air. If you wish to learn more about catalytic converters, this article will help. 

What Does a Bad Catalytic Converter Sound Like?

A bad catalytic converter sound can take many forms depending on the issue you’re dealing with. The catalysts inside the converter will continue working almost indefinitely. 

However, an oil buildup or engine misfire will lead to damage on the inside and, combined with physical wear, it will lead the catalytic converter to fail. When that happens, you will be able to hear it. Here’s a list of bad catalytic converter sounds: 

Catalytic Converter Rattle

A catalytic converter rattle that sounds like it’s coming from under your car means that you’re dealing with a bad catalytic converter. It’s one of the telltale signs. The rattle will be more intense when the catalytic converter is cold, but as the temperature rises, it may become more difficult to hear. 

Knocking or Ticking Sound

If you’re hearing a knocking or ticking sound coming from your catalytic converter, there may be several reasons for it. Such as an exhaust leak, in which case the noise will intensify when you accelerate. You should keep in mind that some cars will make this kind of sound when idle, but it may not be cause for alarm. 

In case you’re experiencing lifter tick noisealternator noisebad wheel bearing sound, differential whine noise, clunking noise we have got that covered too.

Causes of Catalytic Converter Rattle Noise

If you hear your catalytic converter rattle, it could mean it’s time to replace it. To determine that, you must pinpoint the cause of the rattle. Now, that may be due to two reasons and we will discuss them in-depth. 

Loose Heat Shield

If the heat shield is loose, it will lead to a catalytic converter rattle. This is pretty common when one or more bolts either loosen up, break, or become corroded. When this happens, the heat shield will move around and it will rattle when the car is in motion. 

You could remove the heat shield, but that would lead to excessive heat transfer to the cab compartment of your car. Not to mention, it could lead to a fire hazard if you drive over dry grass or leaves. 

That means that if you’re dealing with a loose heat shield, you must tighten it immediately, repair the bolts if needed, or replace the bolts if they’re too corroded. Here’s a video that will help you fix the issue if you’re dealing with a loose heat shield. 

Damaged Ceramic Honeycomb Structure

If the catalytic converter rattle is present when you accelerate, it could be due to a damaged or broken ceramic honeycomb structure. The ceramic honeycomb structure can become damaged through wear over time or due to physical damage from direct impact to the cat. 

Though you may not be able to fix the ceramic honeycomb structure, there’s an easy solution you can try. Take a hammer and tap on the catalytic converter until you know where the rattle is coming from. Then, insert a screw in that spot. 

The screw will penetrate the ceramic honeycomb structure and keep it in place so you don’t have to deal with the catalytic converter rattle anymore. Of course, this is only a temporary solution that will allow you to get more miles out of your catalytic converter. Eventually, you will have to replace it. 

Signs of a Bad Catalytic Converter

A bad catalytic converter sound is not the only symptom! Many other signs will indicate your catalytic converter is reaching the finish line. Knowing what these symptoms are will help you prepare for the impending failure of the cat and also help you understand what’s going on a lot better. Here are the symptoms you should look out for: 

Poor Engine Performance

Poor engine performance is one of the main signs your catalytic converter is going bad. Whether that’s poor acceleration, rough idle, or issues when starting your car, it all means that there’s a problem with the catalytic converter. It could be that the cat is clogged and the exhaust is not flowing as it should, or there could be a crack, leading the exhaust to leak. 

Catalytic Converter Rattle

If you hear a catalytic converter, that’s the right sign something is not right with the cat. As explained before, this could be due to an issue with the heat shield or honeycomb of the catalytic converter. Either way, it tells you that you will have to replace this part sooner than you thought. 

“Check Engine” Light 

Whenever there’s something wrong with your car, it will let you know thanks to all the warning systems in place. If your “check engine” light comes on, it means something is going on with the catalytic converter. Use an OBD2 to check the code and see what’s the issue. If you’re missing the OBD2, you can go to your local auto parts store and ask them to check the codes for you. 

You Smell a Rotten Egg

If you smell a rotten egg or a sulfuric kind of smell coming from the exhaust of your car, you’ll know you’re dealing with a bad catalytic converter. If the smoke coming out of the tailpipe is dark, that’s another clear sign that your cat is starting to die. 

Bad Gas Mileage 

If your catalytic converter is going bad, your car won’t only not perform well, it will also have bad gas mileage. That’s a big indication that the system is not being efficient at all, which means the cat is either clogged or reaching the end of its lifespan. 

Failed Emissions Test

Last but not least, a failed emissions test is another clear sign that your catalytic converter is going bad. Remember, the job of the cat is to remove pollutants from the exhaust. An emissions test will let you know whether this part is doing its job or not and the people at the emissions station will point out the issue for you. 

How to Fix a Bad Catalytic Converter Sound Without Replacing It

Now that you understand the causes and the symptoms of a bad catalytic converter, let’s talk about how you can fix a catalytic converter rattle without having to replace the part. There are many things you can do to get more use out of your catalytic converter, reduce or eliminate the rattle, and save some money in the process. 

Clean the Catalytic Converter 

One of the easiest things you can do to reduce or even eliminate catalytic converter noise is to clean it. As time goes by, buildup will be generated in the cat and lead to a blockage, which can cause not only noise but also poor performance. Now, there are three methods you can use to get your catalytic converter squeaky clean: 

Method 1: Use Sodium Hydroxide

You can clean your catalytic converter using sodium hydroxide, which you can find on Amazon. We recommend this one from Belle Chemical! Now, the first thing you have to do is remove the catalytic converter from your car and soak the inside of the cat with sodium hydroxide. Use a spray bottle for this and make sure you get both sides. 

Once the inside of the catalytic converter is soaked thoroughly, let it sit for 20 minutes or more so the chemicals can do their job. Then, rinse it out thoroughly from both sides. Make sure you get everything out, so consider using a hose and take your time. Lastly, let it dry before you put it back in your car. If you need a visual aid, this video can help. 

Method 2: Use Lacquer Thinner

Another way to get your catalytic converter clean is to use lacquer thinner. This is a very easy method because all you have to do is add a gallon of lacquer thinner to your gas tank. Make sure there are 10 gallons of gas in there. Then, drive your car for 150 miles while keeping the RPMs on 2500 or more for at least half an hour. 

This will get the lacquer thinner to work through the entire system. Once that happens, your catalytic converter rattle will hopefully disappear and you will also enjoy better performance. We recommend the Klean-Strip Green Lacquer Thinner and here’s a video of the process in case you need a visual guide. 

Method 3: Use High-Octane Fuel and Additives

Lastly, you can use high-octane fuel and additives to clean your catalytic converter. It may seem too easy, but using higher-quality gas can make a big difference. If you usually use low octane fuel, try high octane a few times and you may notice an improvement. 

High octane fuel will increase airflow and sometimes that’s enough to reduce or eliminate catalytic converter rattle. Similarly, fuel additives can help you clean the catalytic converter and all you have to do is add them to your gas tank. We recommend the Lucas LUC10013 Fuel Treatment for this. 

Repair the Heat Shield on the Catalytic Converter

As we mentioned before, a loose heat shield is one of the main causes of catalytic converter noise. To fix it, you have to remove the heat shield, which is very easy. All you must do is remove a few bolts and you may need a bit of penetrating oil because the bolts can be difficult to remove. 

Once the bolts are off, you can wash the heat shield with soap and water and if you notice the inside is hazy, use high-grit sandpaper to polish it. Before you reinstall the heat shield back on, make sure you add a bit of anti-seize compound to the bolts and tighten them following torque specifications. 

How to Replace a Bad Catalytic Converter

Replacing a bad catalytic converter is expensive, so many people wonder if it’s not something they can do on their own. Well, you’ll be happy to know it’s not very complicated. As long as you make sure you purchase a catalytic converter that’s specific to your car’s make and model so you only have to bolt it in. If you purchase a universal cat, welding is required for installation. 

The first thing you have to do to replace a bad catalytic converter is to remove the old one. Apply some penetrating oil on the bolts and give it a second before you use a socket wrench to remove them. Then, install your new cat by setting it in place and inserting the bolts. 

Make sure you douse some anti-seize compound to each bolt before you insert them and make sure you wrench them down to the proper torque specification. That’s it! The replacement is easy enough and it will save you good money, just make sure you get the right cat and do your research to get ready. Here’s a full guide to help you get familiar with the process.

What is the average cost of catalytic converter replacement?

On average, replacing a catalytic converter will cost you anywhere between $600 and $2,000, so it’s definitely not cheap. You have to pay for the new cat and also pay for labor. You can save money by installing the part yourself, which is not difficult at all. If you know how to use the tools and you get familiar with the process, you won’t have an issue and you will save up to $200 on labor alone. 

Can a clogged catalytic converter cause rough idle?

Yes, a clogged catalytic converter can cause rough idle. In fact, it’s one of the symptoms of a bad cat, along with reduced power, hesitation from the engine when you want to accelerate, and difficulty starting the car or not being able to start the vehicle at all. 

To determine if you’re dealing with a clogged cat, you can perform the vacuum test, the backpressure test, or the temperature test. To unclog your cat, refer back to the section on how to fix a bad catalytic without replacing it. There, we provide 3 different methods so you can clean your cat and reduce or eliminate catalytic converter rattle. 

How to use Cataclean catalytic converter cleaner?

Cataclean Liquid Science is a product that’s very simple to use and it can restore your catalytic converter. All you have to do to use this cleaner is to remove the seal and empty the contents of one bottle into your fuel tank, making sure that there are at least 15 liters of gas in the tank. Lastly, go for a drive for 15 to 30 minutes, and that’s it! Refuel whenever you must.

Can I unclog my catalytic converter without detaching it?

If your catalytic converter is clogged, you have to clean it. You can do that with a catalytic converter cleaner like Cataclean, use sodium hydroxide, lacquer thinner, or start using high octane fuel or a fuel additive. Please refer back to our section on how to fix a catalytic converter without replacing it to learn more about how to clean a catalytic converter. 

Can a bad catalytic converter cause a misfire?

Yes, it can. In fact, an engine misfire is a symptom of a catalytic converter that needs to be replaced. When the cat gets clogged, it will overheat easily and cause quite a bit of damage to your engine. If you can’t replace your cat right away, consider cleaning it so you can unclog it and keep it from overheating. 

How hot do catalytic converters get?

On average, a catalytic converter can run up to 1200 to 1600 degrees Fahrenheit or 650 to 870 degrees Celsius. If your catalytic converter overheats, it can go over 2000 degrees Fahrenheit or 1093 degrees Celsius, which can be very dangerous for many different reasons. 

If you have read this guide and you consider that your bad catalytic converter is on its last legs, take it to a mechanic for a professional opinion ASAP, consider replacing the cat, or at least keep it unclogged and clean so you can avoid big safety issues. 

How long does a catalytic converter last?

In theory, the catalysts inside the converter can last forever. However, many other factors may lead your catalytic converter to fail or become inefficient in its function. 

For example, a lean fuel mixture can lead to clogs, and a clogged catalytic converter can lead to many of the issues we’ve discussed in this guide. Similarly, a misfiring cylinder can make the catalytic converter overheat and greatly reduce its lifespan. If nothing ever happens, your cat will continue working forever. 

Can you drive with a bad catalytic converter?

Though driving with a bad catalytic converter is not too dangerous, it’s not recommended. In fact, it’s not legal to drive a car that’s giving off higher emissions than the state allows. So, if you have a bad catalytic converter, do your best to repair it ASAP or replace it if necessary so you can avoid issues on the road and with the law. 

Does catalytic converter cleaner work?

Catalytic converter cleaner will help you keep your cat clean and unclogged, so it does what it’s supposed to do. However, catalytic converter cleaners are not a long-term solution and they won’t repair your cat. They don’t eliminate the problem, they just help you improve the symptoms of a bad catalytic converter, so keep that in mind and adjust your expectations accordingly. 

Closing Words

Catalytic converters do a very important job, but the second that you start hearing a catalytic converter rattle, you must do something about it. Today’s guide provided short-term solutions so you can manage the symptoms of a bad catalytic converter for as long as possible before you have to replace it. However, don’t wait too long! Replacing your cat will be expensive, but it will be worth it. 

Leave a Comment