I have a situation. In a historic home previously wired, with distributed audio Russound CAV. we have a very loud and present buzz or hum (never changes tone or level). The layout: distrib audio to master bedroom to a russound A-B amplifier that senses voltage because there is a local monitor with no internal speakers but has speaker outs. 16-4 from the tv audio out to a high-low converter with built-in ground isolation then to the A-B switch. the 2 speakers located in the room are for distributed audio and to watch TV. the buzz went away after we installed the high-low converter. now the buzz is back. it only occurs when you activate the distributed audio via keypad and when you turn the keypad off it remains until you power the A-B switch all the way down. we were getting hum from an outlet associated with the CAV and have sense had a dedicated outlet ran. This was all hooked up the same time as the high-low converter. it was without hum for nearly a month and know that the homeowner has moved in it is present again. I thought it could be because of the owner plugging something into an outlet, but its a dedicated circuit (tested to be). anyone had similar problems if so what was the cure. or anyone have any ideas. we have swapped equipment, power conditioners, and sources still a buzz, humm!!!

If, in fact, it is a buzz from a ground loop you might try lifting the ground on the power to each device one at a time and see if it goes away.  That’s what the recording studio engineers taught me.

-Morgan