Ground Loop?

Cleeds is correct. At 20 awg, you aren’t even close to a 20 amp code requirement. For a 20 amp circuit, you should have at a minimum, 12 awg wire. Personally, if this was a custom job, I would run 10 awg stranded wire in metal flex conduit. Again, I’m not a certified electrician but you may have much bigger problems than the ground. How long is the run of AQ 20 awg wire? Is the AQ wire rated for 20 amps at the length of your run? For your sake, I hope the electrician verified all the specs before installing the two circuits. Worse case scenario, one or more wires will heat up and possibly cause a short or fire.

I want to thank everyone for their input. It’s not 20 gauge now that I think more about it, it was done 12 years ago and the 10 gage sounds more familiar. The wire was made for this application. I had an electrician install the wire, breakers and receptacles to code. The run is only about 10-15 feet at most. Even so I plugged 1 at a time into a regular receptacle, 1 in the dedicated line and 1 in the regular socket then both with no change. So, I don’t think it’s in the dedicated receptacle and another regular outlet do the same thing. I’ll get my neighbor to check ground and stuff, he knows more about A/C than I do.

I’m so glad! When I read 20 awg, my heart sank. If you used audio receptacles, check the ground requirements. If interconnects are running to a device on a different ground, this may be the source of the ground loop. Hope you figure things out. Have a great weekend!

I was pretty sure the OP meant 20A wiring, so I just skipped right over that. :) 

I had similar problem with a preamp. The solution was purchasing an isolation transformer.