Yea I checked a bunch of stuff to narrow it down. Lisence plate frame, wing, then kinda narrowed it down to the rear plastic hopefully this will do the trick for you. You can also check the wing bolts for tightness while you have the plastic off.
I can take it back off tomorrow after work and get some pics or video. When I originally did it, it was one of those Sat afternoons that I had nothing to do and figured I would fix the rattle. I found a video or thread with someone explaining how it comes off which helped.
I will get some stuff to you tomorrow. My rattle was coming from the passanger rear hatch area. Is yours the same.