Not the seatbelt rattle... this is the rods that run lengthwise across the width of the trunk under the rear deck. One of them vibrates/rattles when driving over rough surfaces. There is a lot of movement inside that white plastic clip in the center that keeps the rods separated, is that normal? Any ideas on how to fix?

 

Those rods are torsion springs that pop your trunk open. Just wrap something around one of the springs in the middle of it so you won't have the rattle. Anything you want, an old rag if you want to.

 

I went to a hardware store and got some sticky on one side insulating wrap for water pipes and wrapped the hell out of all of the bars. I was going insane from the rattle the sub in the trunk was creating.

 

Great ideas, thanks! I found that the white clip in the middle was broken so hopefully a new one will help as well.