On one leg or two legs?

Ozzy,
I run them balanced

Maril -- Do try what I suggested with a battery-powered portable AM radio, checking to see how much interference or buzz it picks up in the room, and if it is significant, walking around with the radio to try to track down its source.

How close are your nearest neighbors -- maybe it's coming from them.

Aside from interference being picked up through the air, the one other possibility that occurs to me, given that the amps worked fine before being moved to your house, is that perhaps the mechanical jostling that occurred during the move affected something within the amps. Such as, perhaps, a screw loosening slightly, causing the contact between a metal transformer housing and the chassis to lose its integrity.

-- Al

I'll try radio

I would take the noisier of the two amps back to your friends house and have him connect it to one of his speakers...... Take along the power cord and the speaker cable. Take along your multimeter too.

If it does not hum/buzz there, &^#@$%#@, Check the voltage at the wall outlet he plugged the amp into. See if the voltage is lower than yours.

Are these amps self biasing?

Actually, I just wanted to post about something I did last night-
I moved amps L to R, and the hum moved as well, but I have also noticed, that a level is lower on the side of a humming amp (center image moved to the opposite side),
I double- checked moving it back, there is disbalance.
So now I'm strongly suspecting there is something buzzing inside the amp. I'm going to ask my friend, if he wants to take it to BAT for check- up.
Question- what internally can cause this kind of buzzing?
Cap, resistor, bad tube?
Amps are self biasing