I'm having the same issue. Pretty much don't have rattles but when it gets cold my rear cabin area has creaking and a fair amount of noise when hitting bumps in the road. No rattles (like loose clip rattles) but seems like the creaking its just everywhere! Similar to vinyl rubbing in vinyl. I did a physical inspection of my back are and it seems like the c pillar interior trim (next to the back seats) make a similar noise against the rubber door molding where it overlaps. I pressed on the moldings and they move slightly. I saw on a Bimmer forum that the rubber can be treated, so I'm going to try that before I get to the other vibration/creaking noises that the cabin makes. I've watched a ton of youtube videos and couldn't find anything similar to what I and yourself seem to be experiencing. I came from a Lexus and the interior creaking was NON EXISTENT. It's bothering me!