Top 9 Ways on How to Quiet a Rattling Catalytic Converter

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If your catalytic converter rattles, it’s a symptom that it may be worn out or damaged internally from excess rich fuel mixtures.

Additionally, the catalytic converter can fail when the honeycomb meshes on the inside break or collapse apart.

Rattling noises that arise from your car can cause what the Centers of Disease Control term as Cognitive Distraction.

According to statistics, in the U.S., over 2800 were killed and approximately 400,000 injured as a result of distracted driving.

In this article, I shall be discussing the common symptoms of a failing converter and different ways to fix the problem.

What is a Catalytic Converter?

A catalytic converter is a device that helps control the pollutants and toxic gases contained in exhaust gas into less harmful pollutants.

The harmful compounds in this case are:

  • Carbon monoxide
  • Hydrocarbons
  • Nitrogen Oxides

The carbon monoxide is converted into carbon dioxide through a redox reaction, while nitrogen oxide is converted into nitrogen and oxygen; lastly, the hydrocarbons are converted into water and carbon dioxide.

Essentially, when these toxic compounds from the engine reach the catalytic converter, they’re forced through an inner honeycomb lined with catalysts that spark a series of chemical reactions.

This converts the toxic compounds to fewer toxic compounds.

What Does a Bad Catalytic Converter Sound Like?

Rattling noises.

If you hear rattling sounds coming from underneath your car, it could be possible that the catalytic converter is damaged. Honeycomb mesh could be broken or collapsed.

When you switch on the ignition, these pieces of broken honeycomb mesh will vibrate, resulting in rattling noises. The damage could be as a result of age or simply from excessively rich fuel mixtures. And lastly the rattling noise will become worse over time.

catalytic converter rattles

Popping Noise. Typically, a popping sound when accelerating is caused by a blockage in the cat converter that restricts exhaust flow and causes back pressure.

Noise during Acceleration. Typically, a rattling that intensifies as the car speeds indicates that the ceramic honeycomb of the cat converter has come loose or broken into pieces.

Ticking Sounds. The ticking sound might result from oil, gasoline, or even engine coolant being burned by the converter. The noise may occur at a cold start, idling, or acceleration, and it may also be caused by a converter leak.

Pinging Sound. Pinging may indicate obstruction due to age, fuel pollution, or overheating.

Knocking Noise. A cat’s knocking might suggest a leak or result from a broken heat shield.

What Causes Catalytic Converter Rattle

Cracked Honeycomb Structure

Over time, the ceramic honeycomb structure is likely to get damaged. You may have crushed it against an object on the road, especially for low-riding cars, and broken it unintentionally while driving, causing the broken pieces to rattle.

On the other hand, the high temperatures within the converter can cause the honeycomb-like structure to break, which may be audible when the various parts of the converter move. In rare instances, the heat also might fuse honeycomb components, or they may get obstructed by buildup.

Problems with the honeycomb structure can cause engine failure and severe damage to your vehicle; thus, they must be repaired as soon as possible to prevent further damage.

Loose Heat Shield

Every catalytic converter features a heat shield to protect the vehicle’s floor from the intense temperatures generated by the converter. Without it, the heat may be sufficient to melt through it and cause more damage.

Typically, the heat shield is attached with screws; with time, the screws may loosen, get corroded, or even break off. This will result in the heat shield rubbing against the car’s floor as you drive. If the rattling noise is louder as the vehicle increases speed, then there is likelihood of something loose in your car exhaust system.

A loose catalytic converter heat shield is not something that you should worry about. However, driving with it may lead it to grow loose and finally fall off, so you should fix it immediately to avoid aggravating the situation.

What are the Signs of a Failing Catalytic Converter?

The are several tell-tale signs of a failing catalytic converter that you should watch out for. They include:

  • Check Engine Light: If your check engine light is on and you are sure that it’s not a problem to do with the oxygen sensor, emission-related code, or engine misfire, then have your mechanic check your cat converter.
  • Misfiring: a faulty or missing cat will cause gasoline in the engine to heat up to the point that it actually ignites. Misfiring can damage the engine, and you should make sure that your mechanic checks the engine.
  • Rattling noises from underneath the vehicle: a rattling sound from beneath your vehicle is never a good sign. When a cat converter is damaged, it can cause the mesh honeycomb to collapse or break. After turning on your vehicle, these pieces will vibrate and rattle.
  • Decrease gas mileage: if the gas mileage has significantly dropped, it could a sign of a clogged catalytic converter or other mechanical problems on your car. A clogged catalytic results to reduced airflow that causes the engine to burn extra fuel. This not only makes it a pain at the pump but also makes the clog worse.
  • Dark smoke and rotten egg smell: a clogged converter makes it hard for exhaust to exit your car, resulting in a thicker and darker build-up. Because fuel contains sulfates characterized by rotten egg smell, a clogged catalytic converter causes buildup that makes the undetectable odor detectable.
  • Failed Emission Test: several states here in the USA have laws requiring a diagnostic check to pass the emissions test. If the cat is faulty, the test will fail.

What Are the 3 Most Leading Failures of a Catalytic Converter?

Well, converters never fail on their own, and failure indicates a symptom of a larger problem.

That’s why it’s always important to figure out the main cause of the failure and perform the repair before installing a new converter.

Catalytic converter failures can be categorized into three:

  • Structural damage
  • Overheated or broken converters
  • Oil-fouled/coated substrate

The main cause of the structural damage to the cat is road debris.

Visual inspection on the converter shield will indicate some structural impact. Other possible causes include

  • Thermal shock
  • Corrosion
  • Missing O2 sensors
  • Stress fractures

Any malfunction resulting from unusual high 02 and CO or HC levels entering the converter will significantly spike the temperatures.

Some possible culprits for high HC include:

  • Low compression
  • Misfires
  • AFR cylinder imbalance
  • Poor spark or no spark

The oil-fouled substrate, also known as catalyst poisoning main occurs when the converter is exposed to emission containing compounds that coat the surfaces until it no longer functions well.

There are several causes of oil-fouled substrate build-up, and they include:

  • Internal coolant leaks
  • Improper additives or fuels
  • Excess carbon buildup in the exhaust
  • Excessive oil consumption

How to Quiet a Rattling Catalytic Converter

Whether it’s clogged or faulty, there are several ways you can make the catalytic converter quieter. Below are methods to help you reactivate the old one and make it perform like new.

How to Stop the Rattles

When your catalytic converter is going to fail, it will cause rattling noises.If you regularly inspect it, the chances are that it won’t fall apart, and you’ll be in a position to repair it before it’s too late.

However, you will need a mechanics stethoscope to identify the loose pieces inside the system.

To fix the loose parts, drill a hole at each location that’s affected and insert a drywall screw in it. This screw will hold the loose par s in place, stopping the rattling and extending the converter’s lifespan.

Regularly Clean It

You should check regularly the catalytic converter for carbon build-up and mild oil fouling and clean it.

Something like Cataclean 120007 Complete Engine will cost you less than $30.

Simply mix it with the gasoline, and it will remove those toxic deposits from the engine and converter as well.

However, if the cleaner doesn’t solve the problem, it’s most likely to be clogged with sulfur and phosphorous from the fuel and oil.

According to research soaking the converter in dilute citric acid will remove harmful deposits with affecting platinum inside the converter.

Use Lacquer Thinner

Lacquer thinner is a highly effective tool for cleaning clogged catalytic converter before it loses efficiency.

Simply add one gallon of the cat cleaner to the gas tank and then top up 10 gallons of gasoline.

Likewise,  you should then drive the car for approximately 150miles and keep the RPM at 2500 or higher for about 30 minutes.

After the lacquer has worked its magic, you should expect improved performance, and if possible, the rattling shouldn’t be anymore.

Fuel additives are can also be great lifesavers- check out my guide on the best additives to the quiet engine and catalytic converters.

Tighten the Heat Shield

If a loosened heat shield is causing the rattling, the only solution is to tighten it. Or else, it could fall off or trap tiny pebbles between itself and the converter, resulting in an even louder rattling. Luckily, this is a straightforward fix.

Remove all rusted bolts. I would recommend a penetrating oil or WD-40. Clean the heat shield and cat converter’s body using sandpaper as required.

Replace the shield in its original position and use fresh bolts to secure it. Tighten everything to prevent it from becoming loose again. If the shield is destroyed, you may need to replace it, so be prepared for the cost. Hopefully, it won’t come to that, and you’ll be able to eliminate the noise with a few easy actions.

Clean the Converter with Sodium Hydroxide

If the exhaust from your vehicle smells like rotten eggs, the converter is not oxidizing the hydrogen sulfide into odorless sulfur dioxide. The accumulation of residue can jam chambers and generate rattling. If you are technically savvy, you should remove and clean the converter.

Sodium hydroxide will eliminate hydrogen sulfide. Pour it into a spray bottle and liberally cover the inside honeycomb by spraying it into the converter. Utilize a drip basin or a bucket to perform the cleaning. Allow the sodium hydroxide to function for a minimum of 20 to 30 minutes.

After the sodium hydroxide has accomplished its purpose, thoroughly rinse the inside with water. To flush out the chemicals, use a garden water hose and flush out jammed debris inside the cat.

Use High-Quality Fuel

Most individuals have short commutes, which do not generate sufficient heat to eliminate carbon buildup or residue in the converter. A catalyst converter is intended to work within particular temperature ranges, like an engine. In the past, if an engine developed carbon buildup, all you needed was a long drive on the highway to get rid of the carbon.

Similarly, to prevent residue building in the catalytic converter, making the engine work even harder for a few hours multiple times each month or more is prudent. Before starting your engine, filling the gas tank with premium, high-octane fuel is advisable. Before refueling, the gasoline tank should be almost empty, not nearly full.

Low-quality, low-octane gasoline generates greater buildup in the engine & cat, while high-quality, high-octane fuel causes less buildup and fewer issues.

This gasoline is much more costly, but it will save you money over time. It is less expensive than a new cat converter and can improve gas mileage and eliminate other potential issues.

Some gasoline additives assist in removing and minimizing residue accumulation in the converter and the engine.

Get a New Catalytic Converter

Additionally, if everything else fails, you will have to dig deeper into your pockets and get a new cat.

You can install the converter yourself, but here is what you should do- purchase a direct fit converter and not a universal fit.

This is because universal fit requires welding while a direct fit only requires bolts. Below is another video on how to DIY installation.

Final thoughts

Above are the best methods on how to deal with catalytic converter rattles to achieve quieter rides.

Lastly, fixing the cat helps reduce air pollution and sound pollution, achieving quiet rides and reducing possible distractions on the highway.


1 thought on “Top 9 Ways on How to Quiet a Rattling Catalytic Converter”

  1. I used Cataclean once, then again. I was skeptical – the price was $25.00 but I went forward and after the purchase followed the directions. It went into a 2004 Tundr C.C. 2WD V8 SR5 with 175K mi. on it. I wanted to put a load on the engine while using tthis stuff so I drove up Angeles Crest since I live nearby. I do remember the trcuk feeling a bit more peppier once back in town. Now it’s been a couple years and my D side Cat is rattling. The cost for a new one is around $1,500.00! so Now that $25.00 doesn’t seem so bad. I’ll give it another go tomorrow – fingers crossed! If it’s anything like a creosote log … should work out ok.


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