We love cars of all shapes and sizes, and have a firm rule to never ever autobody-shame our fellow car enthusiasts. Real vehicles have curves, and we’ll be the first to admit we like a little junk in our car trunks.

But unfortunately, that junk can lead to sound distortion, rattling, and unwanted noise. Your trunk can not only let exhaust noise and tire noise leak in, but can also cause unwanted sounds from rattling, loose parts, and even your beloved subwoofer.

Luckily the trunk is one of the easier spaces to apply sound deadening and sound blocking material, think of it as Spanx for your car - keeping everything in place and absorbing all the vibration (maybe we should work on our analogies).

Soundproofing your trunk will go a long way to better car audio and a quieter cabin.

We love cars of all shapes and sizes, and have a firm rule to never ever autobody-shame our fellow car enthusiasts. Real vehicles have curves, and we’ll be the first to admit we like a little junk in our car trunks.

But unfortunately, that junk can lead to sound distortion, rattling, and unwanted noise. Your trunk can not only let exhaust noise and tire noise leak in, but can also cause unwanted sounds from rattling, loose parts, and even your beloved subwoofer.

Luckily the trunk is one of the easier spaces to apply sound deadening and sound blocking material, think of it as Spanx for your car - keeping everything in place and absorbing all the vibration (maybe we should work on our analogies).

Soundproofing your trunk will go a long way to better car audio and a quieter cabin.

Much like your car door sound deadening project, the trunk is essentially an echo chamber made of metal panels with little or no insulation - we're talking some plastic paneling and thin carpet. Any flat or flimsy metal panel is going to vibrate and create structural noise. Look inside your trunk and what do you see? Big, flat quarter panels. A big sheet of metal as the trunk floor pan and covering the wheel wells. Top that off with a trunk lid that's often light, hollow, and not always firmly attached. You see a trunk. We see one of the loudest parts of your vehicle.

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For a quiet trunk you have to stop the noise from coming in AND stop your trunk from creating noise. We offer several trunk insulation kits to make this as easy as possible. Each kit enables you to create two layers - the sound deadening layer, and the sound blocking layer. But before you add, you must take away...

STEP 1: Prepping Your Trunk

Before you get started, remove absolutely everything from your trunk and rear deck to get all the way down to the metal panels. This means taking out the spare tire, carpets, and trunk card (cardboard or carpet that covers the entire trunk floor pan). Carefully strip the walls of your trunk to expose the interior quarter panel and your trunk lid. The trunk lid is often forgotten, but it's one of the most important places to apply sound damping material, especially if you have a subwoofer. Don't forget the vibrations that comes from your trunk lid bouncing and clashing with the closure as you drive along the highway. Deadening the trunk lid is especially important if you have a subwoofer.

If you run into wiring, do your best to safely tuck it into enclosures to keep it out of the way. If that doesn’t seem possible, decide whether you need to temporarily remove the wiring or if you would be able to work around it.

STEP 2: The Sound Deadening Layer

You may be surprised to learn that most trunks are between 15 and 30 square feet. Ensure you have the right amount of butyl rubber sound deadening material for your space (never use asphalt!). Trunks are full of nooks and crannies so when dealing with tricky areas we recommend using a sharp utility knife to cut your deadening material down to smaller squares to make it easier to apply. Sound deadener is most effective if it’s fully adhered to your trunk, so apply firmly using a hand roller.

Cover at least 60% of the trunk, walls, rear deck, and lid with sound deadener. Focus coverage on the wheel wells as that’s the source of a lot of vibration. If you have a subwoofer, you should cover 100% of the trunk, including the lid. You also may want to use a decoupling foam, like OverKill Pro, to prevent the rear deck lid from rattling or bumping your back window. This is because your trunk is subject to much stronger vibrations then it would face from normal rattling and road noise.

INSTALLATION TIPS

If you decide not to cover 100% of the metal surface, put the bulk of the trunk sound deadener on the flatter, flimsier metal sheets. The curved parts of the trunk are more structurally sound and tend to rattle less.

If you're trying to conserve sound dampening material, use the checkerboard approach highlighted in Mark from CarAudioFabrication's video build.

STEP 3: The Sound Blocking Layer

Imagine unwanted noise is a thunderstorm. While sound deadening material only needs to go on some of the structure to keep your house from rattling, the only way to stay dry is to be fully covered from the rain. If you want to keep noise from raining on your parade, apply mass loaded vinyl for cars to the entire floor and walls of your trunk. There are 2 approaches to this.

One of the easier methods is to adhere our Luxury Liner Pro to the cardboard shelf or carpet that covers your spare tire. This gives you a template to know exactly how much material is required, and allows you to remove the material as needed. As long as the trunk is fully covered and the foam side faces down, you will get adequate sound blocking.

If you want to be thorough, the best way to keep out road noise is to apply sound blocking material directly over your sound deadening material. It’s super important that you get FULL coverage, use foil tape to seal any gaps. External noise will leak through any opening it can find.

Note that most cars have a ‘relief vent’ in the trunk. This is a flap that equalizes the pressure when you close your trunk. DO NOT cover the vent! If you do, you may not be able to close your trunk anymore (physics is crazy).

Next time you’re cruising along trying to enjoy your favorite song but can’t ignore the buzz caused by your subwoofer, the road noise from your tires, or that awful drone of your exhaust, remember the culprit - the trunk. Luckily with the right materials and a little time, you CAN get rid of that rattle and road noise, and all you’ll be left with is good vibrations.

If you want to talk through your build and how to get better car audio, give us a call or shoot us a message. We'll help you get the results you want!

Call us at 1.866.570.5440