I have not found out yet what it was? But I think the rubber bump stop might be the fix as my cousin has it on his and I dont have it on mine. Now its not the rubber bump stops to the left and right of the deck lid, its the one right beside the latch. Here is a pic of the BMW diagram. If you study it there is a BUMP STOP listed the replaces one of the torex screws that holds the rear latch in place. Its number 38 on the diagram. I dont have it on mine but, when my cousin got his back from BMW, it had this item in place. I cant even find the part number on the BMW system so, I guess it was introduced as the "FIX" for the rattle, so ask you dealer about it. It should only cost a few pennies and you could install yourself
