Dynamat worth it ? - quoted $450 from audio shop

SouthArk370Z

After I had the interior panels re-installed after installing the sound damping, but without spare/sub/carpet, the cabin was pretty noisy. The damping material helped a lot, but it was still noisier than no damping with spare/sub/carpet. Put everything back in the car and it was much quieter than without damping. So, yeah, I'd say that something like a thicker pad under the carpet would help.
You can install sound damping in the floor of the hatch area without doing any major dis-assembly of the interior. Should have the same (or better) effect than thicker pad/carpet. Covering the strut towers and wheel wells will do more good but you have to remove interior panels.

ScottIN is right about the back glass - great sound reflector. Nice if you have a Bose sub but terrible for road noise. Some internal louvers might help but there's not a lot you can do about it.

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