I have taken my car in numerous times and complained that my rear deck was rattling. Well a while back I traced the source to the middle seat belt. I finally took the whole seat belt assembly out and that fixed the rattle. I am going to take apart the seat belt assembly tonight and try to do a quick fix. So for now I only have a 4 passenger vehicle.

 

Look in the HOW TO section on the stickies, it is in there. There is a way to fix it. I dont have the problem since the whole sub was removed.

Dixit