I guess I would have to describe it as a drone/loud humm type noise. It does it only under WOT, and only when the car is in gear. At first I thought exhaust leak, but no noise when I rev while in neutral. The catatlytic converter is new, so I ruled out a clogged cat. Also, I have Hedman headers and their y-pipe, so the exhaust has to make pretty much a 90 degree bend to clear the SFCs. Not sure if that could cause it or not.

 

tire, something in the drive line, or exhaust vibration

 

Forget to add something:

There is also a noticeable bog/power loss when this happens. For example, downshifting from 3rd to 2nd at about 30 mph under WOT. It'll make the noise, bog, then finally go.