You could be getting some hum through the interconnects from some other device that is not on the dedicated circuit, or a ground loop caused by differences in ground between the circuit the amp is on and the circuit the other equipment is on (if you are hearing a radio station in the hum, I'd think the former is more likely than the latter). Cable TV's always a troublesome one, too. An even easier possibility? Interconnects lying on power cords can pick up some weird stuff sometimes.

------------------
gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review