Catalytic Converter Noises: Best Ways To Identify and Fix

Catalytic converter noises are a complete annoyance for many car owners suffering from this problem. The catalytic converter helps to reduce the harmful emissions that can leave your car to the environment.

Catalytic Converter Rattle 5 Ways To Fix the Noise

Loose heat shields and residue are some of the common reasons for the rattling noises. In this article, our car repair experts discuss how to fix the problem.

What Are the Causes of Catalytic Converter Rattle Noise?

The causes of a catalytic converter’s rattling noise are a loose or unfastened heat shield and a damaged or broken honeycomb structure. Another significant cause of the catalytic converter’s rattle noise is accumulated residue of debris, dirt, carbon, and hydrogen sulfide.

– Unfastened Heat Shield

An unfastened heat shield can be the reason the catalytic converter makes noise. The shield in a catalytic converter lowers interior temperatures and protects transmissions from excessive heat. The shield is placed over the catalytic converter to act as a barrier and protect other components from its excess heat.

When the heat shield becomes unfastened, the catalytic converter rattles. Often made of stainless steel, a heat shield will become loose if one or more bolts are damaged, corroded, or loose. Thus, it is bound to shake and rattle when the vehicle is in motion.

If the shield is loose, it will be unable to prevent foreign materials from entering the converter. The presence of foreign objects can result in bad catalytic converters, which will rattle while driving. Also, these materials can result in a clogged catalytic converter, reducing its efficiency and allowing it to make noise whenever the car is in motion.

Removing the heat shield to stop the noise could lead to excessive heat transfer to the cab compartment of the vehicle. It could also cause a fire hazard if you drive the vehicle over dry grass or leaves. Besides the catalytic converter sound, a damaged converter produces a rotten egg smell while driving. It also causes failed emissions tests.

– Broken Ceramic Honeycomb Structure

A converter is made up of a porous honeycomb ceramic base material coated with a precious metal catalyst. The function of the structure is to provide a high catalyst surface area that maximizes the contact between the catalyst and the pollutants in the hot exhaust gases.

The ceramic structure helps the converter to perform its function of cleaning poisonous gases produced during combustion. If the ceramic structure is damaged, the converter will rattle when the car accelerates. The damage can result from wear, physical impact, excessive engine vibration, and corrosion.

Problems with the Catalytic Converter Rattle

When the honeycomb structure is damaged, gaps are created. These gaps become escape routes for exhaust gases, causing the converter to rattle. Thus, if an emission test is carried out, the converter will fail.

The cracked structure pieces will likely rattle when the vehicle accelerates. The cracked or disintegrated pieces can be due to excessive heat, and their continued rattling can cause bad catalytic converters and severe engine problems.

Furthermore, the accumulation of residue will clog the catalysts and prevent airflow in the converter, leading to overheating. The overheating of the converter can damage and melt some components of the converter. If this happens, more blockages will be created, leading to a bad engine or greater engine damage.

– Accumulated Residue

A buildup of residue can be why your converter makes noise while driving. Over time, debris, dirt, carbon, hydrogen sulfide, and other residues would accumulate inside a catalytic converter. The residual buildup will clog the converter, affecting its efficiency and making it a failing catalytic converter.

If your converter’s efficiency reduces, it will rattle when the vehicle is in motion. Also, the residual buildup can result from leaked oil, excessively rich fuel mixtures, low-grade fuel, and burnt coolant. These materials can obstruct the converter and prevent it from performing its functions.

In addition, if your converter fails to perform its primary operation of converting exhaust gases properly, residues will build up in the catalysts. The residues will then create barriers that will cause the converter to rattle. Furthermore, it can degenerate into poor engine performance or reduced engine performance, and engine misfires.

How Can You Fix Rattling Catalytic Converters?

You can fix a catalytic converter that rattles by cleaning the converter using NaOH and thinner, repairing the faulty converter parts, and replacing the heat shield. Another method that you can use to fix the rattle is to replace the converter entirely.

– Clean Converter Using Sodium Hydroxide (NaOH)

By cleaning the catalytic converter, you can lower or eliminate its rattle. One way to clean the converter is to use NaOH. To use this method, you must remove the converter from the car and soak it with NaOH. For this method to be effective, it is advised that you use a spray bottle so that you will get every side.

After ensuring that the insides of the converter are properly soaked, leave it for 20 minutes or more to allow the chemicals to act upon the converter. The next step is to rinse it thoroughly on all sides. In this case, you should use a hose to get everything out.

Finally, let it dry before returning it to the vehicle. Cleaning the converter with NaOH helps remove the accumulated residues that cause blockage. Hence, the converter will no longer make rattling sounds when in motion.

– Clean the Converter Using a Lacquer Thinner

Using a thinner to clean the converter is another effective means of fixing the converter’s rattle. To carry out this method, you will need a gallon of the thinner, which you will add to your gas tank. Ensure that the car has 10 gallons of gas (or fuel). Afterwards, drive your vehicle to 150 miles while keeping the RPMs on 2,500 and more for at least thirty minutes.

Ways to Fix your Catalytic Converter Rattle

The vehicle’s motion will cause the thinner to work through the system. The purpose of the high-temperature engine workout is to burn off the residual buildup clogging the converter and engine. Once this is completed, the converter’s rattle will cease, and you can enjoy your vehicle without worry.

– Use High Octane Fuel and Additives To Clean the Converter

You can clean the converter using fuels with high-octane properties and additives. The use of a higher-quality gas can be effective in cleaning the catalytic converter of residual buildup. If your car uses fuel with low-octane properties, try using high-octane fuels for some time. You will likely notice that the rattle will be reduced.

The use of this fuel type will increase the airflow, which will help to lower the converter’s rattle. In some cases, the rattle can be eliminated. The fuel protects the car engine by dissolving carbon buildup, leading to a clear catalytic converter. Furthermore, fuel with high-octane properties may improve gas mileage and stop other related engine noises.

Also, fuel additives help clean the rattling catalytic converter. To make this happen, you need to add the chemicals inside the fuel tank. Then, it will clean the converter while driving, hopefully eliminating the rattling.

– Fix the Defective Heat Shield

You can fix loose heat shields through repair. First, you must remove the heat shield, which you can do by loosening a few bolts. Now, some bolts can be difficult to remove. If this is the case, you will have to use penetrating oil, which makes the bolts easier to loosen.

While removing the shield, ensure you don’t damage the heat flanges. The bluish tinge you see is a sign of excessive heating. Also, it indicates a blockage in the converter’s chambers.

After removing the bolts, wash the shield using soap and water. The inside of the shield may be hazy, so you try using high-grit sandpaper when polishing the surface. Once you are done cleaning the shield, the next step is to install it back.

Add some anti-seize compound to the bolts before reinstalling the shield. Also, the bolts should be tightened based on torque specifications. Removing and cleaning the shield help eliminate stones and pebbles that may be trapped between the shield and its stainless-steel housing. Also, repairing the shield helps to reduce the catalytic converter’s heat.

There is a possibility that the shield’s welded flanges are faulty, which will affect the converter’s heat. If so, try using galvanized strap clamps to fasten the shield. Later, however, you may replace the catalytic converter heat shield with a new one.

– Clean the Converter With Exhaust Cleaner and Cataclean Fuel

Exhaust cleaner and Cataclean fuel are effective grease and oil removers for engines. Using Cataclean fuel helps to remove the accumulated residue and carbon buildup in a failing converter. It can also remove residual buildup in cylinder heads, fuel injectors, oxygen sensors, and tappets.

Before using this method, make sure you have at least four gallons of fuel. After that, pour about 16 oz of Cataclean into your fuel tank. Then drive the vehicle for about 15-20 minutes so that the cleaner will penetrate inside the engine and converter. The next step is to clear your check engine light after the drive if it is still on.

Drive to the gas station and fill the fuel tank with some fresh fuel. Then drive the car for 50 miles at least. You will notice the cleared check engine light. You will also find that the engine is performing better, and the fuel efficiency is greater because of the Cataclean fuel.

Also, the rattling caused by the clogging of the converter should stop. As a car owner, cleaning with Cataclean fuel every few months will help protect your converter from clogging caused by carbon buildup.

– Clean the Converter Using Sea Foam SS14

Sea Foam SS14 is another effective cleaning agent that removes residual deposits in a converter. Sea Foam SS14 is an EPA-registered 12 oz aerosol foam that eliminates carbon and other deposits from converters, pistons, combustion chambers, valves, and oxygen sensors. By removing the residual buildup, the aerosol foam improves the performance of a defective engine, its efficiency, and the emissions of the engine components.

To use Sea Foam SS14, run the engine until the intake is warm, then turn it off. Take out the air filter and restart the engine. Then put the end of the injector tube in the carburetor throat and squirt 2 to 4 oz in short bursts to avoid stalling. A long burst should follow it before you turn the engine off.

After that, allow the engine to rest for 10 minutes before you run it for another ten or more minutes. The Sea Foam SS14 helps to burn off any residue that is acting as a blockage. When you check the engine, you should notice improved performance.

– Repair Defective Parts of the Converter

A damaged converter can be repaired by replacing its faulty parts. Repairing the converter is a cost-effective means of eliminating the rattling sound.

However, some converter parts, like honeycomb monoliths, cannot be repaired if damaged. If some components are badly damaged, you must replace the entire converter with a new one. After carrying out the catalytic converter replacement, you will notice that the converter’s sound is much better.

– Change the Converter

A typical catalytic converter lasts as long as the car. However, most converters do not, as they wear over time. Many converters fail after a vehicle nears the 100,000-mile mark. Consult with a professional to replace the old converter with a new one.

When you replace the converter and carry out an emission test, you will notice that the converter is releasing less harmful gases into the environment.

Frequently Asked Questions

– Is It Safe To Drive a Car With a Catalytic Converter That Rattles?

Yes, it is mostly safe to drive a car with a catalytic converter that rattles, but it is not advisable. Besides harming the environment, driving the car may further damage the converter. But if the rattling is due to residual buildup, driving it may not damage the engine.

– Do Cars Accelerate Faster Without Catalytic Converters?

Yes, cars accelerate faster without a catalytic converter. However, it is not a safe option. In addition, although it is believed that removing the converter improves fuel consumption and exhaust sound, it is still illegal in many states in the U.S.

– What Are the Most Common Noises From a Damaged Catalytic Converter?

The most common noises from a damaged catalytic converter include popping, knocking, and pinging. Each type of noise represents a different converter problem. It is advisable to find the cause of the noise as soon as you hear it and fix it before it damages other car parts.

– What Is the Replacement Cost for a Catalytic Converter?

The replacement cost for a catalytic converter ranges between $800 and $2,200. The cost you will incur depends on varying factors such as car makes and models and the type of car engine. Car owners with large engines tend to pay more to replace their vehicle’s converter.

End the Noise of your Catalytic Converter Rattle

Is a Noisy Catalytic Converter a Possible Cause of a Car Making Noise After the Engine is Turned Off?

A car noise after engine turned off could potentially be caused by a noisy catalytic converter. This emission control device, located in the exhaust system, can sometimes develop internal problems, such as a broken or dislodged catalyst. When the car is turned off, the excess heat in the converter can cause it to emit unusual sounds. If you suspect this is the issue, it’s advisable to have it inspected and repaired by a qualified mechanic.


Having read this article, you now have a better understanding of catalytic converter rattle and ways to fix the noise.

Let’s summarize the main points so far and share some final thoughts:

  • Residual buildup in a converter can be fixed by cleaning it with sodium hydroxide or lacquer thinner.
  • High-octane fuels and additives can clean a converter and improve the engine’s performance.
  • Cataclean fuel and exhaust cleaner effectively removes oil and grease buildup in the converter.
  • Repairing the faulty parts of a converter can help reduce or eliminate the rattling noise.
  • Repairing a defective heat shield helps to clean accumulated residues and stop rattling noise.

There’s no need to worry about the rattling of your catalytic converter. Simply follow the guidelines in this article to help you troubleshoot and fix the rattling noise of your converter.


5/5 - (15 votes)
Ran When Parked