Did you try a 3 prong to 2 prong cheater to lift any grounds? Also if you have a cable box in that system/ room unplug it and the coax to it while troubleshooting
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.