Catalytic Converter Rattle: How to Quiet a Rattling Catalytic Converter [2023]

After driving for thousands of miles you may notice rattling sounds coming from underneath your vehicle.

A catalytic converter rattle can have you experiencing a wide array of symptoms including loss of performance and switching your check engine light on.

Replacing this part can get quite expensive so before doing so, you may want to figure out a few ways to quiet a rattling catalytic converter.

So if you are interested in finding out the ways, continue reading as we explore these and discuss the symptoms that your vehicle can experience when your catalytic converter rattles.

Most of these technicians can be performed at home and are very affordable so let’s get right into it.

What is a catalytic converter?

So before we jump into this article, if you don’t already know what a catalytic converter is, then let me explain.

The catalytic converter is a part of your exhaust system.

During the fuel combustion process where engines create power, pollutants are released into the air by way of your exhaust.

Some of these pollutants like carbon monoxide, nitrogen oxides, and hydrocarbons are bad for the environment.

Your catalytic converter uses catalysts which creates a chemical reaction to neutralize the harmful pollutants.

This unit is made up of three main parts, namely the heat shield, shell or casing, and the high flow honeycomb catalyst.

The catalytic converter heat shield prevents the high temperatures from escaping and surrounds the entire unit.

The shell or caring is what houses all the other parts of the catalytic converter that are responsible for performing the chemical reactions.

The high flow honeycomb catalyst is the pathways mimicking a honeycomb design

On the walls of these pathways, some catalysts are responsible for creating the chemical reactions and reducing harmful pollutants from being released into the air.

How does a catalytic converter work?

When your catalytic converter is functioning properly, it reduces the number of harmful pollutants your vehicle releases into the air.

The exhaust enters the catalytic converter and travels through the inner honeycombs where the walls are lined with catalysts.

The catalysts then activate and the chemical reaction converts harmful pollutants.

There are two main types of catalysts that control this reaction.

They are the oxidation catalysts and reduction catalysts.

The oxidation catalyst converts carbon monoxide and hydrocarbons to carbon dioxide and water.

On the other hand, the reduction catalyst breaks down nitrogen oxide into nitrogen and oxygen.

What does a bad catalytic converter sound like?

After converting tons and tons of exhaust, your catalytic converter can suffer from external wear.

While the inside may still work after a long period, external components can cause several issues.

If something goes wrong, you may be able to hear it.

So what does a bad catalytic converter sound like?

Below are some sounds you need to be on the lookout for.

Rattling sounds

A rattling sound from under your car could very well be because of your catalytic converter.

If it is indeed the catalytic converter, you should be hearing the rattling noise louder when it’s cold.

Ticking or knocking sounds

Ticking or knocking sound can be a result of either of two things.

Some vehicles make this sound when idle so it may not be a catalytic converter issue.

On the other side of things, this type of noise can be heard if there is a leak in the exhaust.

One way to tell is if the catalytic converter noise when accelerating greatly increases.

Catalytic converter rattle: possible causes

So what causes your catalytic converter to rattle?

Let’s discuss the possible causes.

Loose heat shield

One of the most common culprits of the catalytic converter noise is a loose heat shield.

Sometimes the rattle is due to a bolt holding it in place coming loose or breaking off or is severely corroded.

When that happens, the heat shield moves around resulting in a rattling sound.

This can be potentially dangerous since the heat shield keeps the high temperatures locked into the catalytic converter.

Without the heat shield, excessive heat can be transferred to the inside of your car and it can start a fire if you drive on dry leaves or grass.

Honeycomb structure breaks

The honeycomb structure is made from ceramic and can be damaged over normal wear over time or from physical damage to the catalytic converter.

If that happens, then you need to replace the entire unit.

Signs to look for if hearing a bad catalytic converter sound

If your catalytic converter is making sounds, it may alert you in various ways that something is wrong.

In this section, we’ll talk about the signs you need to look for if your catalytic converter is going bad.

Poor engine performance 

Decreased engine performance of your vehicles is a sure way to tell if your catalytic converter is failing.

Signs to look for are poor acceleration, a rough idle, or if the vehicle won’t start.

A cracked catalytic converter will leak harmful gases and a clogged one will restrict exhaust flow all of which will directly affect the engine performance.

Sounds

As mentioned before, if the catalytic converter is going bad, you can hear rattling ticking, or knocking sounds.

These can be caused by many factors and needs to be checked out asap.

Check Engine Light switches on

The ever-dreaded Check Engine Light will switch on if something is wrong with your catalytic converter.

Vehicles today are equipped with sensors that monitor the efficiency of the converter.

The air-fuel ratio sensor and the oxygen sensor track gas levels in the exhaust system and if something is amiss, it switches on the Check Engine Light.

Do note that this light can switch on for a myriad of issues so it’s best to visit your mechanic to rule out other dangerous issues.

Sulfur smell

If you experience a smell similar to rotten eggs then a bad catalytic converter is the source.

Hydrogen sulfide is produced during the engine combustion process and the catalysts convert it into odorless sulfur dioxide.

If the catalytic converter is going bad, it will stop converting the hydrogen sulfide resulting in the sulfuric smell you experience.

Your exhaust pipe will also give off dark smoke.

Reduced Gas Mileage

Poor engine performance will also mean reduced gas mileage.

If you’ve noticed a reduction in gas mileage, it is a good indication that your catalytic converter is clogged or failing.

Failed emission test

An emission test is administered to check if your catalytic converter is functioning properly. 

This test is required in some states and is one of the best ways to tell if your catalytic converter is working well or failing.

Of course, if your vehicle fails the test it means something is wrong with the catalytic converter.

Fortunately, those administering the test will be able to tell you exactly what the problem is before leaving the emissions station.

Ways to quiet a catalytic converter rattling

So the big question remains which begs to be answered.

Is it possible to quiet a catalytic converter rattling?

The answer is yes, you may be able to do so.

The following methods that are stated below may be able to save your catalytic converter.

However, in extreme cases, you will have no choice but to replace the entire unit.

1. Clean the catalytic converter

One sure and easy way to quiet a catalytic converter is by cleaning it.

The buildup can cause the unit to fail due to the blockage of airflow.

This can result in annoying sounds and poor performance.

Cleaning the unit is very easy and simply requires purchasing a complete fuel system cleaner or using sodium hydroxide.

A fuel system cleaner will clean other parts of the fuel system and not just the catalytic converter as opposed to using sodium hydroxide.

If you are going to use sodium hydroxide, here’s what you need to do.

Remove the catalytic converter from the vehicle before doing anything else.

Take a spray bottle with the sodium hydroxide mixture and spray it into the catalytic converter from both sides.

Give it some time for the chemicals to work and clean up the build-up.

30 minutes should be enough but if you can give it some more time, do that.

Once the chemicals have worked their magic, rinse the unit thoroughly.

If using a fuel system cleaner, here’s a good one to go with.

• Cleans entire fuel system and gets rid of buildup
• Restores performance and power
• Use every 3000 miles

2. Use high-quality gas

If you have a habit of using the lowest octane gas available, using a few tanks of high-quality gas may fix catalytic converter issues.

Doing so may increase airflow and reduce or stop the rattling sounds.

3. Use additives

You can also purchase additives that can clean the catalytic converter.

All you do is pour these additives in your gas tank with gas and as you drive they work their way through the system cleaning as they go.

• reduces hydrocarbon emissions by 50 percent
• prevents carbon build-up
• Improves overall performance 

4. Fixing a loose heat shield

A loose heat shield due to broken, corroded, or lost screws is the number one culprit for excessive rattling coming from under your vehicle.

Remove the rest of the screws keeping the heat shield in place and wash the catalytic converter with soap and water.

To take it one step further you can use some high grit sandpaper and polish it to ensure maximum heat reflection.

After that reinstall using a new screw or screws and tighten to the proper torque specifications.

• Variety pack(3000, 5000,7000 grit)
• Wet and dry use
• High quality

5. Replace the unit

If all else fails then you have no option but to replace the entire catalytic converter.

It isn’t a very hard fix but if you are not too confident, let your mechanic perform this task.

If you think you’ve got this, then here are the steps to changing the catalytic converter by yourself.

First and foremost, purchase a replacement unit that matches your vehicle.

Universal units will need to be welded on and I doubt you’ll want to be welding or have welding tools at home.

A catalytic converter matching your vehicle’s specification can be attached using bolts which is easier to do by yourself instead of welding.

The screws holding your damaged catalytic converter can be a little tough to lose.

Douse the bolts with some penetrating oil to loosen them up.

Let the oil work for a little while before you attempt to unscrew the bolts.

Next, take your socket wrench and remove all the bolts.

Just like removing the unit, installing the new replacement is just as easy.

Before bolting you can try spraying some anti-seize compound on the bolts so they’ll loosen easier next time you need to replace the catalytic converter.

Line the unit up and bolt in place ensuring that you tighten according to the proper torque specifications.

• blend of aluminum, copper and graphite lubricants
• salt, corrosion and moisture resistant
• Prevents galling, corrosion and seizing

What is the estimated lifespan of a catalytic converter?

The lifespan of a catalytic converter could be forever if not for other factors that cause it to fail.

However, other factors such as physical and internal damages are the reason catalytic converters fail.

These include a fuel mixture that’s too lean that can easily cause it to clog or a misfiring cylinder can cause it to overheat thus shortening its lifespan.

Likewise, physical damage like cracks to the unit or broken honeycomb pathways can also shorten a catalytic converter lifespan.

What can I do to minimize issues with my catalytic converter?

Replacing your catalytic converter is quite expensive so if you are interested in the ways you can help to minimize damage, stick around.

To prolong the life of your catalytic converter, switch to high octane gas.

This gas is much cleaner and will not create as much buildup as lower quality octane gas.

If you are using low-quality gas, you can switch to high-quality gas and it may be able to clean out your entire system and continuous use can prevent buildup over time.

Another thing you want to do is to take your vehicle for regular maintenance.

This not only helps to detect problems with your catalytic converter but also identifies problems with other parts of your vehicle that may need immediate attention.

These can include lifter tick issues or wheel bearing making noise troubles.

For more, read our lifter tick and how long will a wheel bearing last after it starts making noise posts.

These both are serious issues that can lead to disaster if they aren’t looked at immediately.

It is always better to be safe than sorry.

If you see that your Check Engine Light is switched on, get to your mechanic asap, it could mean nothing and it could mean something is seriously wrong.

Last but not least, don’t leave your car inactive for extended periods.

Try to at least drive your vehicle once a week at highway speeds for 20 minutes.

This allows the vehicle to reach its operating temperature which ensures your catalytic converter stays working as it should.

If your state stipulates that you need a quiet muffler, check out this quiet performance muffler post.