It seems many of us have this same problem. I too have completely taken apart the entire back seat and shelf (just this weekend again) to no avail. I can isolate it and stop it when riding in the back seat by placing my hand on the shelf at a certain area, but when I remove the shelf, can't find anything that would rattle. I have loaded it up with peices of foam insulation, duct taped some of the clips, etc. Please, Please let me know if you find it!! Thanks.