the best way to find out if there's anything loose is to get under the car and wiggle thing's around.i had a rattle coming up through the shifter hole.turn's out the little tab that holds the air tube to the h-pipe broke.the air tube was rattling against the body.moved the tube alittle,no more rattle.jack the car up,place it on jack stands and look around.
just saw your other post.make sure your tailpipes are not hitting the body.