Best thing to do: take it in to the dealer, a problem like that should be covered under your warranty.
What I would do: Take off the part that you think is rattling and make a minor positioning adjustment when you reinstall it. Usually rattles like you are describing are something extremely minor and can be fixed as easily as shifting the plastic. I had an S-10 that the dash board would squeek, but only when it was very cold out. Wierd huh? I shoved a bundled up peice of tape in between two plastic panels and it stopped.