Backseat buzzing solved (Seat belt retractor?)
 

My brz has been buzzing from the rear passenger side for months. It would get really loud over rough road. Finally had someone sit back there and the sound would change if they yanked the seat belt in and out. So in the trunk I pulled back the lining and wedged a nice mixing bowl between the Seat belt retractor and the frame. Noise is gone! I'll have to have the dealer look at it whenever I go in next.

I heard that buzzing sound coming from my back seat this morning while driving to work. Going to check out the back seat belt tonight.
Thanks for the information:bow:.