My situation was really weird...I would hear a "popping" noise occasionally from the rear area, but couldn't develop a pattern. Sometimes it would "pop" while sitting absolutely still. I kept looking and one day discovered that the interior trim in the hatch area looked loose around one edge. Upon investigation, the "plugs" that pop into the metal holding the trim had come loose. As I tried to "pop" them back in place, a few more came loose! The dealer confirmed that the parts had failed and ordered more from Germany. They were able to pop the trim back in place somewhat, but I'm still waiting on the parts to arrive. It's no big deal...just weird.

Fritz