There is a Guild punch line to this question, but it's a sound system issue and I'm hoping one of the many techies here may have a quick answer. I've attached a (rough) drawing of my home studio. Apologies that some lines are power and some are signal and I don't differentiate, but hopefully it's obvious what's what. My Tone King MK II Imperial amp has a loud buzz, 60 Hz I assume. My Fender Princeton '65 reissue amp does not. The buzz disappears if I'm holding the guitar and touch a vocal mic at the same time. All devices are on the same Furman "power conditioning" power strip. If I unplug everything on the circuit breaker and only plug in the amp, the buzz exists. The Tone King buzzes to a varying degree with all my guitars except my Guild X-500, which is dead quiet. Thanks in advance for any suggestions.