ya what reinke said......foam tape and dynamat...best around....also, is it also your deck lid? i had the same problem and i dynamted my entire trunk and lid and siliconed parts of the tail lights....and also, in the trunk, under the back deck, your speakers and mounts i guarantee are loose as hell...i got in my trunk and checked that out right away....take a bottle of silicone, some foam tape, and some dynamat in with you....and you could prolly make a days worth of work out of findin stuff that rattles and that needs to be siliconed or taped...make sure you find it all before you put your dynamat up though...
