Hey KC_Mike. It's likely that the rattle is coming from subsonic signals...or close to, say the 20-40 Hz range. I was able to lock down a rattle by using Rives Audio Test CD 2 (http://www.rivesaudio.com/software/softframes.html). I played the cd @ the 20 Hz signal and was able to easily pinpoint the rattle as there was no other sounds disrupting me.

It was funny...its was a bathroom mirror down the hall and around the corner. Now thats impressive bass!

"We're on the island of Misfit Toys"