Try lifting the ground at the preamp power cable.
Ground only the component which draws the most AC current and lift it for all the other components.
Ground passing through line and cables at the same time can induce ground loops.
McIntosh MC 2106: HUM!!!
Hi. Please give reasons WHY. It’s out of both speakers, suddenly yesterday when I disconnected/ connected , more/ less components. Thank you….
all internal components were replaced. Fuse is solid.Sorry 2105 model.