Intermittent low hum/buzz

Thx ,Jea48 I found it today (again) I swapped out the rca interconnects between the pre amp and the power amp. They’re was a pair of Kimbers in there before and I switched them out for an old budget pair of Adioquests. So possibly its a shielding thing the Kimbers have none or its caused by the cables being run through the wall or both.The home run circuit that powers the system is not running anywhere near this space but there is one or more existing circuits in that wall between the family room and the master bedroom.I just ran those Adioquests outside the wall as a quick test so I don’t really know for sure yet or I could be completely out to lunch on the whole theory because it’s intermittent, It’s frustrating, thats why I say “ I found it again “ I’ve been into Hi Fi since I was a teen but only vacum tubes for three years or so I’ve got a complete solid state system as well so I could also change out the pre and power amps to rule those out per your suggestion also ,thx again Jea48.

I had a hum for over a year and tried everything.  Spent $750 for a guy to come to my house to check everything and he could not figure it out.  Then I tried a $80 dollar Hum X and the problem is gone.

HUM X does help but for my system it was renamed HUM-(minus) because while there was a perceptible diminishing of hum it wasn't gone, The improvement was well worth the $50 bucks I paid. For what its worth a solid clay brick on top of the transformer cage cooled the hum too but since hum is vibration I noticed additional clarity in playback overall. The Mad Scientists Tube toppers helped also. 3 pair on top of the three sets of preamp tubes. More resolution as well. By passed the Furman power stripe which cleared the tunes a little and also took out a trance amount of hum. Hum is a remarkably resilient little demon. Plus, my room is so quiet that an ant walking behind my sub causes a quavering in the treble.