No question in my mind - it's a ground fault conflict. If I were there I believe I could isolate the problem fairly easily, but unfortunately, you are 1200 miles away. Wish I could be of more assistance.

Gary cool
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!

K+E=W (Knowledge Plus Experience = Wisdom.)