[JakeJ]

I am in alignment with DaveC113 and DWG.  I think you should identify the source of the problem first (utility or home) then solve.  I was going to suggest a whole house isolation transformer if it is the utility but it might be a bad a pole pig.  The PP 15 may solve the issue but if the incoming power is a problem then I would be concerned it would eventually get worse and cause problems with the PP 15.

Just some thoughts.

[darkstar_xiii]

How did the PS Audio Power Plat 15 workout for you, did it solve the problem?

[Big Red Machine]

If you leave the sheet music out in front of the gear, they might learn the words and stop the humming.

Or do what DWG said. Cheaper to have an electrician come out and check you out than trash your gear.

And those ISO trannies are not wildly expensive - Ebay to try one perhaps.

[Rusty Jefferson]

How did the PS Audio Power Plat 15 workout for you, did it solve the problem?

Haven't heard back from the OP about success eliminating the hum. There was another similar thread running recently with someone having the same issue and finding a resolution.
https://www.audiocircle.com/index.php?topic=172903.0

[aln]

You may want to try one of these from van alstine - HUMDINGER DC LINE BLOCKER.  Good luck!