sealing holes most likely wont stop rattle.. there are a few things.. there are these little vent things behind the panels in the trunk, usually in the back corner, there is a little ruber flap on there. that thing usually rattles like fucking crazy, the lisence plate. the little loop that sticks up where the truck latches down on, just BARELY losen them, like BARELY, tap it with a hammer just make it move a little bit, like less then 1/16th an inch and tighten it back up, if that doenst work, get some damn cotton or dynomatt if you have the money and start putting it everywhere it looks like metal could be hitting.