How Do You Fix A Noisy Catalytic Converter?

A catalytic converter is an essential emission control device found in the exhaust system of vehicles. It helps convert harmful exhaust gasses into less toxic pollutants. Over time, the catalytic converter can become clogged or damaged, which may cause rattling, vibration, and other noises. If left unchecked, a noisy catalytic converter can lead to reduced fuel efficiency and problems with passing emissions testing.

The good news is, there are several methods to fix a noisy catalytic converter without immediately having to replace the entire system. This article provides an overview of catalytic converter noise, diagnosing the issue, and both short and long-term solutions to quiet a rattling, vibrating catalytic converter.

What Causes Catalytic Converter Noise?

A properly operating catalytic converter should run smoothly and quietly. However, several issues can arise to cause unwelcome noise from the catalytic converter:

Buildup Of Exhaust Contaminants 

Over time, engine oil, fuel additives, carbon deposits, and other contaminants can coat the honeycomb structure inside the catalytic converter. This buildup eventually clogs the pores of the structure, obstructing exhaust flow and often causing rattling noises.

Internal Damage 

The ceramic honeycomb structure inside the catalytic converter is rather fragile. Potholes, debris, and exposure to excessive exhaust temperatures can crack, dislodge, or break apart portions of this structure. Damaged areas will disrupt normal exhaust flow and cause vibration.

Heat Shield Issues 

Most catalytic converters have an attached heat shield to protect surrounding components from the intense heat. If this shield becomes loose or develops holes from rust, it can also cause annoying rattling sounds.

What Causes Catalytic Converter Noise
What Causes Catalytic Converter Noise

Catalyst Deterioration 

The actual catalyst coated on the honeycomb is designed to degrade over time. As its efficiency drops off, exhaust flow becomes more turbulent, leading to noise and vibration.

Accurately diagnosing the root cause of catalytic converter noise is needed to determine the best repair approach.

Diagnosing A Noisy Catalytic Converter

Several tests can help pinpoint the reason behind catalytic converter noise:

Visual Inspection

Pop open the hood and conduct a visual exam of the catalytic converter and surrounding exhaust components. Look for any obvious damage like cracked heat shields or bent/crushed exhaust pipes. Give the various joints and mounts a shake by hand to check for looseness.

Listen to the Noise

Road test the vehicle to listen closely to the noise and try to determine the source. Catalytic converter noise will originate from the center area under the vehicle. Also take note of when the noise occurs – at idle, acceleration, or cruise. This can help identify flow restrictions versus internal damage.

Check Engine Light

Use an OBD2 scanner to check for any diagnostic trouble codes (DTCs) stored in the engine computer. Codes like P0420 or P0430 indicate failing catalytic converter efficiency. While not always accompanied by noise, it points to possible internal catalyst breakdown.

Pressure Test

A shop can verify exhaust back pressure issues with the catalytic converter using a 5-gas exhaust analyzer. High back pressure caused by internal clogging will be obvious on the readings while running tests.

By combining these diagnostic checks, you’ll get a solid handle on why your catalytic converter is noisy and the repair options available.

Short Term Solutions For Noisy Catalytic Converters

The following quick solutions can sometimes temporarily quiet a noisy catalytic converter:

Add High-Quality Fuel Detergent

Fuel injector cleaners containing polyetheramine (PEA) do an excellent job dissolving carbon buildup and deposits on exhaust components like the catalytic converter. Treat the vehicle to a full tank using a premium fuel injector detergent. It may help remove some of the contaminants plugging up the catalyst.

Switch Fuel Octane Rating

Using a lower fuel grade than your engine requires can cause premature catalytic converter failure from runaway pre-ignition and overheating. Filling up with Top Tier premium gasoline for a few tanks can help clean out deposits.

Fix Loose Heat Shield

If diagnosed with a loose converter heat shield, tighten up or replace any broken or missing fastener hardware to stop the rattling against the converter body. A mechanic can re-weld small holes or cracks in the heat shield as well.

Mild Catalyst Cleaners

For stubborn carbon deposits, a mild chemical cleaner like CRC Cataclean can be added to the gas tank when refueling. It helps remove built up soot in the converter over several tank fills. Avoid harsh chemical cleaners that could weaken the catalyst.

These quick tips can potentially extend the life of a noisy catalytic converter and delay a major repair. But once diagnosed with internal damage or catalyst breakdown, a replacement will be required.

Long Term Solutions For A Noisy Catalytic Converter

For persistent rattling noises or confirmed internal converter damage, replacement of the entire catalytic converter assembly is needed to permanently solve the problem. Here are your options:

Diagnosing A Noisy Catalytic Converter
Diagnosing A Noisy Catalytic Converter

Aftermarket Catalytic Converter

Aftermarket catalytic converters from companies like Walker, Eastern, and Magnaflow offer a less expensive replacement alternative over OEM converters. While not identical, aftermarket converters must still meet the same Federal emissions regulations. Just verify the exact fit for your vehicle.

OEM Catalytic Converter

Opting for the same OEM catalytic converter offered by your vehicle manufacturer provides a bolt-in perfect fit replacement. While more costly than aftermarket, OEM converters have the exact same internal specifications and catalyst coating. Some even come with longer warranties when installed by a dealer.

Universal Catalytic Converter

If unable to source a direct-fit catalytic converter for an older or rare vehicle, universal converters are available. They bolt into the existing exhaust piping but require some welding modifications for proper fitment. A muffler shop can custom fabricate and install a universal converter.

Replacing a damaged catalytic converter requires some welding skills and exhaust knowledge. Most drivers will be better off having a professional mechanic or muffler shop handle the entire replacement job.

What Causes A Noisy Catalytic Converter?

A catalytic converter usually becomes noisy when the internal honeycomb structure becomes clogged with carbon deposits or damaged. This obstructs exhaust flow, causing turbulence and vibration. Heat shield damage, loose mounts, and general internal part breakdown can also lead to rattling or vibration noises from the catalytic converter.

What Are 2 Symptoms Of A Failed Catalytic Converter?

Two major symptoms of a failed catalytic converter are 1) reduced engine performance and 2) the illumination of the check engine light. Performance suffers because restricted exhaust flow creates backpressure. 

The engine computer detects the drop in converter efficiency and activates the check engine light. Other symptoms include loud rattling noises, high exhaust temperatures, and failure of emissions testing.

Can I Drive With A Rattling Catalytic Converter?

It’s not recommended to drive long with a rattling catalytic converter. The rattling is a sign of internal damage and reduced performance. Driving in this condition risks further degradation and complete failure. Have the noisy converter inspected and repaired promptly to prevent expensive repairs. Short trips may be ok but avoid extended driving until fixed.

Will Removing Catalytic Converter Harm Engine?

Removing the catalytic converter will not directly damage the engine but it is illegal to drive without one installed. The converter helps reduce toxic emissions for cleaner air. Eliminating it defeats this pollution control. 

You’ll also experience a drop in performance from increased backpressure. Plus, the check engine light will stay on constantly without the proper emissions system intact.

Does Removing Catalytic Converter Increase Power?

Removing the catalytic converter allows for freer exhaust flow which can translate to a slight power gain. But the difference is typically negligible, offset by increased backpressure. 

Any potential power benefits are outweighed by the detrimental effects on emissions and engine efficiency. Most performance gains actually come from upgrading to a higher-flow converter versus fully removing one.


Dealing with a rattling, vibrating catalytic converter is annoying and can’t be ignored. By using the diagnostic tips and short-term solutions outlined in this article, you may be able to postpone needing a catalytic converter replacement. 

But once you confirm internal damage or catalyst breakdown, replacing the entire converter assembly is the only permanent fix for a noisy catalytic converter. With some preventative maintenance and care, your new catalytic converter will last for many years of quiet, eco-friendly driving.

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Ammar Masoud

I have had a long and fulfilling career in the automotive industry, primarily with Honda and Acura. With 15 years of experience as a Honda service technician, I became highly skilled in repair and maintenance, gaining a deep understanding of these vehicles. After many years in the automotive field, I decided to embark on a second career in industrial manufacturing. It was a significant change, but I found that the skills I had honed in the automotive industry were incredibly valuable in my new role. In my current position in industrial manufacturing, the demand for quality workmanship and meticulous attention to detail is paramount. Fortunately, these are traits that I have cultivated throughout my years in the automotive industry. I take pride in applying these skills to meet the high standards expected in the manufacturing sector.