I just installed my straightpipes and the rattling just gets worst. There is a really bad rattle that is coming from the rear of the roof liner. Its at the end, right before the rear window is. If I put my hand and push up on what feels like a plastic piece, the rattles goes away noticably.

The rattle is worst at 3k rpms. If I give it any gas it rattles really fast, like a machine gun going off. Its from 3k to 4k rpms and after wards, its totally gone. Any idea how to fix this??