I 've tried everything and no sound deadening will work, but i'm also running a pair of L7's. I finnaly got rid of it and really boosted my bass by running them in a single-reflex bandpass and brought the ports up to holes on the rear deck. It's louder than hell now (the bass isn't trapped in the trunk) and there is no rattle. No matter what people say you can get great SQ from a bandpass if you build it properly.