Grounding ?

Is a possible fix, and this is JUST a question, that 1 or more pieces has an internal hot/neutral swap?
Could you tell somehow? Maybe have all gear plugged into the wall without any I/Cs. Than measure for voltage between the chassis or ground of each piece? If there is a voltage between chassis of 2 pieces, isn't that a hot/ neutral swap?

Does everyone own an outlet tester? The type w/3 leds to indicate various good / bad conditions?

Bob_R
I believe your statement would be true IF there were no hot/neutral reverse wiring. I do NOT mean the outlet, the condition of which is easily seen with an easily purchased outlet tester, but internal to each piece of gear. Does that make any sense?

There can only be current flow if ground potential is different between each piece. An easy way to determine this would be to plug everything in than measure chassis-2-chassis with a decent DVM.

Given the sensitivity of the gear involved, there doesn't have to be much current, either.

Bob_b
Yes I am paranoid, but that doesn't matter in this case.
My personal system has NO hum or other internal noise issues.

My recommendation is to check NOT to ground, but between system components. IF there is voltage present, I would consider swapping hot/neutral where the power pigtail gets to the first terminal strip or whatever.
Once everything agrees, the hum should disappear?

Exactly, J,
there will be voltage present if the ground plug is used or not! Connecting 2 pieces under these conditions is using 1 of 'em as 'local ground'.

Please explain 'leakage'. I have heard the term but am unfamiliar with its use in this case.

Have I just been lucky all these years in NOT ever having a bigtime hum problem?