Also using outlets/lines for some audio gear that is also powering devices that have some sort of power contol on them like dimmer switches or motors and the like intoduces gound hum.
I played one club where whenever the toilet flushed a loud hum occured in the pa. The reason was the toilet pump was powered off the same power lines as the pa. It was very funny, because after the show got going it was obvious to all, but a few timesin the evening new folks would come in and go to the bathroom. When they came out, everyone knew they just flushed the toilet. We had some fun with that.

Bob
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