Are you using or have you tried balanced (XLR) interconnects?
They worked for me when I had an unwanted hum. I never took the time
to seriously diagnose the cause (lack of patience), I took the advice of Paul
McGowan from PS Audio.
Ground loop hum
My technics turntable developed a ground loop hum when I got a new preamp Rogue RP7 and power amp Aesthetix Atlas. I had a ground wire connected to the turntable and grounded it to each, one after the other when the first had no effect. Neither did the second grounding. It has been suggested I ground it to both at the same time which I haven’t tried yet. Any other suggestions? I am running the system from two dedicated 20 amp lines. Running Vandersteen Quatro wood ct speakers. Thanks in advance.