What else could be causing this hum?
I had been using an RCA-XLR cable to a NU3000DSP without issue, but atfter moving some equipment I needed a longer cable and switched to an RCA-1/4" TRS adapter which introduced a loud buzzing. Things I have tried:
5 different outlets in different rooms with and without cheater plug
Running coax cable through power conditioner and various EMI isolators
Isolating power and speaker cables
Connecting only amp and sub to the receiver
I did mod the amp with a 140mm fan. I thought perhaps the fan motor could be interfering, but removing it changed nothing.
Any suggestions on what else it could be?