I have been working on this for a long time. I have a 96 civic. what I did first was go to my local auto parts store and bought some spray on bedliner ( designed for trucks but very good a sound deadening). I took off my door panels and sprayed that on the backside of the actual plastic panels. I also put that on the backside of my plastic peice in the rear window to help stop speaker rattle. Then I stripped my interior and sprayed that all along the floor under the carpet, then reinstalled everything. It cost me about $10 total (2 cans) and helped a lot. Next on my list is some actuall sound dampening material inside the doors, and some more spray on bedliner in the wheel wells.

but so far it is working really good. :thumbup: