Originally Posted by CeEl
You probably already tried this, but did you open the pass through? made sure it's not the ski bag or the shelves in there? If you can, maybe open and close it from the trunk as well (just be careful, vaguely recall some people reporting that they broke the locking latch mechanism).
I've not opened the pass through, I'll consider that... the sound however sounds right on that flat plastic deck, the bit the roof back area sits on. Its gone a bit quieter since the temps have dropped, but still there.