As a first step I would put a cheater plug on the lower cable to lift the ground and see if it goes away.
What would cause noise (ground noise?) when touching the volume control and tone controls?
I have a new preamp that I recently hooked up and I'm getting some interference or what may be ground noise but I only hear it when I'm physically touching the metal volume knob and tone controls. When I touch the metal top of the case in addition to the knobs, the noise will subside. Just looking for ideas to help isolate the cause. I think the case itself just isn't grounded sufficiently.
I have tried new power cables, RCA cables and plugging into different outlets with no change.