I mean I know this may sound a bit off... but could it be the old rear hatch rattle problem that quite a few people have experienced?

https://www.crossfireforum.org/forum...ear-hatch.html

Damn...I just re-read the post... seems like you already tried to check out the hatch rattle...oh well, back to the drawing board.

Mine actually just started rattling too, but I think mine is the hatch seeing as I don't have Koni's on yet