[Freon]

I have a sort of noise (not sure its a "buzz") as well when the car is actually off. Very strange behavior. It also sounds like there is some emissions/charcoal cansister pump stuff going on under the trunk after I park and lock my car sometimes, so I suspect that is creating some noise in the electrical system that makes its way into the speakers. Still odd that it happens when the car is off and the radio is presumably unpowered.