When done right, the difference is nothing short of amazing!

You can get bulk packs of Dynamat Extreme for half the list price with free shipping from Amazon dot com. You actually don't have to cover the entire surface of the metal for it to be effective either. I learned this from sites regarding installing it on aircraft, where keeping weight down is at a premium. Tap on the surface before, and some strips of Dynamat and tap on it again. If it is still resonating add more strips a few inces away. Once the resonation is cut down, layer some "insulator" material over the entire area and replace the panel, carpet, etc. Be sure to seal the seams with aluminized tape. It will take car of the remaining sound, noise, heat and fumes.

The perfomance and cost effectiveness of this "insulator" material is incredible and there is currently nothing like it available in the auto industy. It's an aircraft product....great stuff! Check it out. I use the thinner double foiled stuff on everything but the floor, which gets the thicker double sided foil. Cut to fit like a dressmaker pattern and tape up the seams. It's easy to remove later on too.

http://www.aircraftspruce.com/catalog/appages/insulator.php


I used Dynamat on the underside of the roof and added the "insulator" material, which I glued on top of it. The headliner still fit perfectly. The difference in sound between tapping on the roof with and without this treatment is huge. Be thoughful about where you put the stuff when it comes to critical attaching points for trim etc.