TestMonkey

Also check your O2 sensor connecting to your cat/TP.

Wydget

Checked the trunk area. The poles have foam on them that keep them from hitting each other. Ive also checked the spare tire and black heat shield between the battery/fusebox and header. I felt the O2 sensor when i was underneath the car a few weeks ago. It didnt feel loose.

TestMonkey

Maybe check the gaskets on the exhaust and TP.
Maybe something crawled into your exhaust

SheDrivesIt

I have the a similar problem at a similar RPM that is intermittent. My problem is with the front hangar on the passenger side exhaust (mine is a Comptech cat back). There is a fair amount of motion and vibration in the exhaust when you rev. The Comptech seems to hang a bit funny and when the front hangar rubber grips the hangar, it causes the front of the muffler to "oil can" rapidly leading to a rattle. Lubing up the hangar and rubber solves the problem -- at least for quite a while.