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Finished installing 80mil Kilmat on the floor and back wall of a 2005 F350 (Diesel) and it has become painfully obvious there is FAR more noise coming through vents in the back wall then I realized.

Normally there is a felted/fiberglass type panel that covers the back wall that hasn't been reinstalled yet but based on how loud it is (sounds like I have a turbo by the back axle) I was curious if there were any tricks I could use to dampen the sound from the vents?

This can't be that uncommon of a problem so hopefully, someone has seen a method that works...Any thoughts?

261575
 

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I used 3m Acoustic Thinsulate to cover those vents. I did cover one with foam+mass loaded vinyl. The other triple 3m coverage. It helped considerably as the factory rear carpet/jute isnt going back in the truck.

Unfortunately those vents are almost essential to air flow inside the cab so they need to be somewhat able to pass air. The fan motor doesnt work as hard and doors close much easier when the vents can breathe.
 

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Yea, I don't want to prevent function but I'm wondering if there is something I can possibly add to the back of the stock felt panel to help soak up the excess noise.

Any preference for the thinsulate or the MLV+Foam for such a scenario?
 

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If you're going to be putting the carpet back then it does a pretty good job honestly. Something that has a compression factor would make it easier to reinstall the oem carpet. 3m acoustic Thinsulate would be that product. Open cell foam has absorption properties as well, though I had trouble finding verified absorption rates for any brand in production.

The foam+mlv is far more effective for the noise, and far more effective at blocking the air movement. Mlv itself is hard to beat for the purpose it serves. Especially in automotive applications. Sheeted lead works well, but that's a personal choice. The 3m is pretty decent honestly. On my newer truck there are areas around the wheel wells that use what I assume to be a fibrous product I can only assume is for sound absorption. I used two layers of the sm400 over the vent and notice a difference in noise that comes through. I'm not sure what quantities you can order the 3m in. I purchased a 20ft roll for use under an older truck headliner and what I had left over I used in the doors and the rear cab wall in a new truck. The 3m is also one of the few products that lists a performance metric for the different thicknesses and types they offer. No snake oil of brand x claiming improvements.

I'd do some mlv+foam with vent cut outs and 3m over the vents. If you intend to reinstall the oem carpet, maybe just the 3m. Mostly for clearance issues of installing mlv+foam and getting the oem carpet to sit as intended. It's more about the unbroken coverage than anything else, and the oem is cut perfectly to size and shaped to eliminate breaks in the sound barrier.
 

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Nope. Not ready to tackle the take it all apart and put it all back together fight. It is tempting though.
 
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