How To Make A Classic Car Quieter (Beginners Guide)

Driving your classic is supposed to be an enjoyable experience, having a constant wall of noise assault you, isn’t my idea of a nice Sunday drive. I’m a mechanic and classic car owner, I’ve tackled this exact problem with my own cars, the solutions are simple and very effective.

So how to make a classic car quieter? The 5 main ways to make a classic car quieter are:

Fit interior insulation
Upgraded the muffler
Fit low profile tires
Replace door and window seals
Spray on under body coating

Modern cars are made to very exact standards, better technology, materials, engineering, and manufacturing means smaller clearances in components and that means a quieter more refined ride.

In this post, we’ll look at fitting insulation to your car to make it whisper quiet. We’ll also look at the main causes of classic car noise and what you can do about it.

Sound Proofing Insulation

Sound insulation isn’t fitted to all cars, higher-end the vehicle will have more and will obviously be quieter. In an effort to save weight and money, cheaper models may have little to none.

Insulation is used for two purposes, suppressing noise and insulates against heat. Noise is a pretty obvious problem, but heat isn’t widely known. Some classic cars will have a catalytic converter fitted close to the underside of the car, as they get older, protective heat shielding can fall off.

The result is excessive heat on the underside of the carpet which causes condensation and then mold.

A well-insulated car will typically have insulation in the following areas:

Cabin floor
Inside doors and trunk lid
Trunk floor
Under hood
Underside of roof

A higher-end car will have a reading in the 50 dB range, whereas a car with no or little insulation may well be in the 75 dB plus area. So there is significant room for improvement.

So the question is, can you DIY this? Yes, most of these insulation suggestions are pretty easy to complete and they don’t all need to be done at once.

What tools will I need? All basic kit, a trim tool would make life easy for removing trim clips. A roller is needed for pressing on the sheets so that the self-adhesive sticks securely. Some screwdrivers, vacuum cleaner, some cardboard, sizer, and some alcohol cleaner.

The soundproofing butyl self-sticking sheets are 2mm thick and come in various sizes, so you’ll have no trouble handling them. However, the sheets are brittle in the cold, so it’s a heated garage or a summertime job. I like the Noico self-adhesive sheets, they’re easy to handle, check them out here on Amazon.

Installing Sound Proofing

Fitting insulation to the cabin floor will make the biggest difference but it will require removing the interior seats and carpets. It’s about two days’ work.

Remove seats and carpets
Vacuum floor
Use cardboard as a template for each floor section
Cut soundproofing sheet to size and test fit
Clean floor with alcohol cleaner
Fit self sticking soundproofing sheet and use roller to secure

Tips:

Have your sheets in a warm environment, it helps keep them pliable
Get a car interior trim tool set, makes life a lot easier removing trim
Be careful not to cover any seat mounting holes
Do use a cardboard template
The next area that brings the most gains – the insides of door-skins. Some cars may have a small sheet already fitted here, but small is the word.

The process is the same as the floor. First, strip the door cover and remove carefully the plastic vapor sheet. Fit the largest sheet you can to the inside of the door skin, using the same method as the floor.

Access won’t be as good, so do what you can. In addition, replacing the outer vapor sheet with insulation works really great, like Rolls Royce great. But you’ll need to be careful not to create problems for yourself by covering up trim holes.

The trunk is the easiest of all, access is usually good and it’s the minimum amount stripping.

The underside of the hood on most cars already has insulation, but sometimes it disintegrates and falls off, checks yours and cut some nicely fitting sheets since it will be seen every time you lift the hood.

Under-Body Insulation

Under-body insulation is a heavy coating sprayed to the underside of your car, not unlike truck bed lining. It protects against rust but also helps insulate against noise. Some cars will have under-coating fitted from new but, usually, it’s a thin coat.

Having the underbody re-coated will greatly improve the sound and heatproofing of the cabin.

The process is simple enough, and you can do it from your garage. But it’s a dirty job because you’ll need to clean the undercarriage before spraying on the material.

Set vehicle on jack stands
Power wash underside of vehicle
Treat any rust with rust eater
Spray on a heavy coat of under-body coating

I wrote a whole post about it here “Classic car under-seal”

The Main Causes Of Car Noise

So what causes all the racket in an old classic car. The noise comes from a few different areas, here’s a list of the main sources.

Exhaust system
Engine
Tires
Wind noise
Interior vibration

Exhaust System Noise

This is the major source of classic car noise. Over time, mufflers lose their ability to absorb sound. The internal insulation and baffles become loose and corroded, they may even contribute to the noise by rattling.

Exhaust systems on old cars are often patch repaired and sometimes mufflers may have been removed.

So what can you do about excessive muffler noise? Have the system checked over, common exhaust problems that will cause noise include:

Loose brackets
Corroded mufflers and pipes
Loose internal muffler baffles and insulation
Broken header bolts
Cracked headers

A broken or corroded exhaust system is a common source of excessive noise, check for the telltale black smoke around exhaust joints and mufflers. Old exhaust systems will need to be repaired, but a small amount of corrosion doesn’t mean you need to change the system.

Consider buying an electric MIG welder and run these repairs yourself. A small household MIG won’t cost a ton, is easy to use, releases your inner MacGyver. Just remember to remove the car battery ground wire before welding. Here’s a pretty neat Lincoln electric MIG welder I seen on Amazon, and the price really surprised me.

Definitely check out my article on welding “Is welding hard to learn?”.

Replacing the complete exhaust system will make a big difference, adding some extra mufflers is another option. Have a pro shop take care of this kind of work, as too many mufflers could create back pressure on the engine, which will cause a loss of power.

Engine Noise

The bulk of the noise comes from the engine itself, older car engines were all bigger, V6 and V8’s, these engines are going to be noisier because they got a lot more going on under the hood than a modern asthmatic four-banger.

Older engines are a very mechanical affair, technology has changed that. Some of the moving parts in a classic car engine have been eliminated and others have been replaced by a quieter electric component.

Engine component clearances in older engines are larger and as the engine wears they get larger again. Larger clearances mean when these metal components come together they make even more noise.

So what can we do to make the engine itself quieter? The simplest things we can do – make sure the engine is maintained and tuned properly.

Have valve clearances checked, it’s a common source of top-end engine noise. One of the most cost-effective ways to quieten an engine is to use a heavier grade engine oil. Heavier oil will muffle the clatter of an older or worn engine.

Tire Noise

Good tires are extremely important, you already know that. Tires can cause lots of noise especially evident at motorway speeds.

As a mechanic, when chasing drive-ability issues, the first place I look is the tires. Often a bad tire can mimic a more serious problem with the steering, wheel bearing, transmission, or differential.

The noise comes from the void inside the tire, it’s amplified and sent through the car via suspension and chassis. Tires with wider spaces and uniform pattern rubber blocks in the tread pattern, tend to create the most road noise.

Wider tires are cool-looking but the downside is more road contact equals more road noise.

All tires aren’t the same of course, All weather, winter, all-terrain, mud terrain all are good at different things. Winter tires for example will have chunkier thread blocks and will be noisier at highway speeds.

Often classic car tires are old and mismatched, apart from a safety issue it will cause excessive road noise.

Check your tires,

How old are they?
Do they match?
Are they all-weather tires?
Are they evenly worn?
Correctly inflated?

In the last few years Pirelli has launched a noise-canceling tire, they added foam to the inside of the tire to absorb the sound. The solution was simple but effective.

Call your local tire specialist and see what he’s got, explain your concerns with tire noise.

Wind Noise

Wind can be a really annoying source of noise, it’s like a constant drone. Figuring it out can be tricky.

Excessive wind noise can be caused by large accessories like mirrors, aerials windows or sunroof shades, hood ornaments, flared arches, etc. Fixing the noise is often a case of removing the accessories and testing.

When I’m chasing a wind noise issue, I try and see if I can find the general area, using wide tape to mask off door openings and windows and testing will often point you in the right direction.

Common causes of wind noise include:

Worn or damaged door seal
Worn or damaged window seal
Damaged sunroof seals
Window out of alignment
Door out of alignment
Body moulding missing
Bulkhead grommets missing

Interior Noise

This is the mother of all irritants, interior squeaks and rattles drive me wild, I must find them, I’m like a cat with a ball of string.

Older cars are squeak central, basically, everything including the dashboard is not as tight as once it was.

It’s an ongoing battle I afraid, I’m always finding new ones to chase. It will require some detective work on your part, but the results will be worth the fight.

Interior irritants range from vibrations, rattles, squeaks, creaking, and banging. Having some silicone spray helps door and window seal noise. The most common reasons for interior trim noises include:

Seat frame damaged or loose
Centre console loose
Dashboard loose
Door cards loose
Dry door seals
Door gubbons loose
Loose window regulators
Door catch out of alignment

Some detective work will point you in the right direction, but having a helper drive the car while you investigate, really shortens the diagnoses time.

Not all rattles and squeaks are interior noises, some are suspension related, here are a few of the more common ones:

Dry/worn suspension bushings
Broken springs
Weak shocks
Worn shock mount bearings