Mach 460 Buzzes what the heck?

I visit the sound shop every once in a while and seems like you guys know your stereo stuff so I figured I'd throw one out. My Mach460 sounds all fine and then if I go over a bump or turn too hard, or stop too fast, I get a loud buzz from the speakers. It is RPM dependednt - gets higher pitched as RPM climbs. Sometimes I can turn off the stereo for a few minutes and it goes away. Other times I have to keep it off for a day or so to go away.

How in the world do I begin to start troubleshooting this? Thanks guys