As a total non techie, is this mainly an issue with older amps or kit? I say this as I have the "play around with different equipment itch" and I have had the humming issue only twice.
The first was putting in an OLD Bryston 4B amp. Eliminated by cutting off the earth prong in the plug.
My current (ha ha) issue is now with a pair of OLD Threshold Nelson Pass monoblocks. The are both buzzing loudly but I suspect that the single ended Audioquest subwoofer cable (the amps do not have balanced inputs) that I put in temporarily may be the issue as I had nowhere to hang the little earth wire. My cable techie has suggest I put in his own built single ended cables which should eliminate the (probable earth) hum. The chances are against BOTH monoblocks being faulty somewhere. I will find out next week when I am next in situ.
The first was putting in an OLD Bryston 4B amp. Eliminated by cutting off the earth prong in the plug.
My current (ha ha) issue is now with a pair of OLD Threshold Nelson Pass monoblocks. The are both buzzing loudly but I suspect that the single ended Audioquest subwoofer cable (the amps do not have balanced inputs) that I put in temporarily may be the issue as I had nowhere to hang the little earth wire. My cable techie has suggest I put in his own built single ended cables which should eliminate the (probable earth) hum. The chances are against BOTH monoblocks being faulty somewhere. I will find out next week when I am next in situ.