ground hum

Hey guys, I have a guitar rig question, not sure if this is the right place to post this question so forgive me if I'm off here. I recently started micing my tube amp in a back room away from the stage so I can crank it getting the tone I want, but still giving the sound guy full volume...

A condition where current circulates in the ground wiring system, due either to the grounds at the end of a length of cable being at different AC potential, or where a video or audio system has multiple paths to ground. Manifests itself usually by varying levels of hum (in audio systems) or...