d'uh!!! stupid me....i think i even participated in that thread.
i think someone else actually had the idea, but i know i did what they said and have been fine ever since. i went to the store and bought some felt furniture pads and stuck them on the trunk lid bump stops.

http://www.keysan.com/pictures/big/tmas1707.jpg

check the tire well. there may be something there loose.

After verifying that my hatch closes securely, I'm now convinced that the rattling is coming from somewhere in the area of the right rear seat. I checked the area for anything loose before leaving work yesterday, and the ride home was quiet. This morning on the way to work, the rattling was back. :confused:
I think it's time to get my wife to drive me around the block a few times riding in the back to hunt down the rattle!

Have a look at the side pillar where you seatbelt originates.

Hope this helps,

Cheers

w/ the felt pads, it's not a matter of the trunk not securing properly. from what i remember about others having the same problem, including myself, our trunks all closed securlely. what the issue was was that the hard rubber bumpers were so hard that it caused the noise. others, including myself, put those felt pads on and have had no rattles since. instead of driving urself nuts over this, i would suggest buying some felt pads and giving that whirl. it's quick, easy and cheap.

Same noise
 

Actually, I have mine narrowed down to coming from within the right rear passenger seatbalk, within the seatback..

I have an aftermarket subwoofer in the back, and when it is pushing it is very clear that this is the origin of the rattle.

nice. congrats on at least narrowing it down at this point. next, all ya gotta do is eliminate it.

Have you ever removed the rear spoiler??

I have the same kind of noise and I think it is coming from the plastic molding on the rear hatch window door. If you open and lift up the rear hatch window.. on the right side (top-inward) of the plastic molding where it meets the glass at the rear section there is a seam in the molding that appears to join two separate pieces. When I put pressure on the seam it is very loose and rattles like the sounds I am hearing.

I haven't been able to verify this but when I do find a way to minimize the gap on the loose seam I'll see if the noise goes away. :dunno:

I think I have the HEAT SHELD issue. How do you suggest securing it? I have what sounds like a minor muffler rattle on acceleration but maybe its the heat sheild.

Oh, by the way the dealer said the exhaust system was OK and the rattle was not coming from that. Of course.