Six Saturdays lost to a ground loop hum I should have caught in an hour

My old rehearsal space in Portland had a hum that drove me nuts for weeks. I blamed my amp, my pedals, the wiring in the whole building. Turns out the fridge on the other side of the wall shared a circuit with my rig. The compressor kicked on and the hum started. I ran an extension cord to a different outlet across the hall and the noise was gone. It was never the gear at all, it was just two things plugged into the same line fighting each other. Two hundred bucks of cables did nothing, a thirty foot cord fixed everything. That taught me to always check the room before I touch the rig.