yep, ground loop.
Your post caused me to relook at a nasty'ism in my own system.
I do not listen to loud music, or, listen to music loud. Its more like background noise, unless I'm ready for a critical listen.
I'd heard a buzzing in my phono circuit, but thought it was normal amplified phonostage noise (I listen at about the 9 o'clock position when I "turn it up", and don't hear the noise until its at the 12 o'clock position. 12 o'clock is at foundation shaking level).
You question had me touching and playing with my tonearms to see if what I was theorizing on was valid.
It wasn't until right then that i realized that I'd been plugged into a nasty dirty circuit. The circuit is tied to an old doorbell transformer that piggybacks off the same outlet, on the opposite of the wall.
A test with a circuit tester revealed a mis-wiring of the outlet.
So I plugged into another circuit, and the hum disappeared - but a buzz replaced it - fark! frustration runs rampant.
I was scratching my head wondering where the heck the buzz came from, when Sarge came in and turned up the kitchen lights, which turned up the buzz as if it were tied to my amplifier gain.
I'd taken an extension cord and run it off the same circuit that feeds the kitchen LED's, and the LED's were causing this new buzzing. As soon as she turned the lights off, the buzz went away, and I have audio normalcy.
Now I just have a pending rewire of the outlet, and removal of the old transformer.
I used to have a dedicated circuit to the rack, but Sarge reclaimed the living room, and i was moved to another wall, that I just found out is nasty dirty.