Remodel causes 60Hz ground loop

Friend remodeled kitchen and when he reconnected entire system, as it had been disassembled and out of harm’s way, he inherited a ground loop.  Small apartment, so moving to another room is not an option.
Only the music server is affected.  Vinyl playback not affected.  Runs everything through Furman 15i Elite conditioner.

Any ideas about approach for ridding the system of this?  Thanks in advance.