If possible, try using balanced interconnects between your amp and preamp.
Yes, if the cause of the problem is along the lines I described, a balanced interface (if your components support that) would most likely resolve it.
That is because with a balanced interface the power amp responds to the difference between the + and - signal inputs, and extraneous ground currents in the cable are ignored (unless they are so severe that they overwhelm the balanced operation, or what is more properly referred to as the common mode rejection capability).
If your components can't run balanced, again I would suggest that you try connecting everything, or at least preamp, power amps, and analog source components, to the same ac port. If that solves the problem, then see what you can move to separate ports without re-introducing the problem.
HTH,
-- Al
