There is for sure a bulletin on a rear hatch rattle (both my 3.0si and 4.8i had a rattle, but more on my 3.0si). It's been a while, but my dealer said something about having to re-align the rear hatch where it closes (or makes contact). It never rattles again.

Also, the Range Rover (which used BMW parts) can rattle. Their (simple) fix was to wrap a small amount of thin, black felt tape around the latch where the glass (upper part of door) makes contact with the lower paft of rear hatch (the one that opens towards you and goes flat). It worked amazing!