If both amps have this hum now that you have moved them, perhaps there is something nearby producing a magnetic field which gives your amps the new hum. You didn't say that it was a 60Hz hum, but that frequency is the most common stray hum in America. Two questions come to my mind: (1) is there a high-powered motor such as an A/C compressor, large blower, or the like which produces a magnetic field in your new location? (2) Is the hum's volume related to the setting of the level controls on the amps? What I am driving at on Question 2 is whether the hum is being introduced through something connected to the amp or whether it is there with the gain down and maybe, if not too difficult, with all input devices disconnected. It sounds like there is either a ground loop somewhere or else the hum is being introduced magnetically somehow from a high-current source somewhere nearby. I would think that new wiring and a new breaker system would be "clean," but don't overlook at least the remote possibility that someone didn't get things grounded well. This one is very rare; but we cannot forget that occasionally even professional workers goof up, though they certainly shouldn't do so. I know of at least one case years ago when a new pipe organ was being installed in an auditorium, and the blower circuit was wired by a professional, and probably a union, electrician; but when the pipe-organ technician came in to power up the instrument, the blower did not come on. It seems the electrician forgot to tie the 220VAC wiring into the main panel! Imagine that! You'd have thought the fellow would have checked for power all the way out to the endpoint specified in his contract. So mistakes definitely do happen, though I would think this one might be the least-likely source of your hum - namely a poor electrical ground.
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