It sounds like a ground problem. Integrated amp, plugged with a cheater ( no ground ) directly to the plug, no inputs, nothing else, and you get a low level buzz that is leaking into the amp circuits.
Perhaps the outlet is wired backwards, it happens. So, the "neutral" is on the wrong side. That can wreck havoc depending how the power supply is designed.
Have you tried other outlets in the house? I think you said you ran one to the kitchen... You can't always trust the electricians.
Get an AC outlet checker at a hardware store. Check to see if the outlet is wired backwards. It's cheap and easy to use. It is possible that your old house was also wired off.
Perhaps the outlet is wired backwards, it happens. So, the "neutral" is on the wrong side. That can wreck havoc depending how the power supply is designed.
Have you tried other outlets in the house? I think you said you ran one to the kitchen... You can't always trust the electricians.
Get an AC outlet checker at a hardware store. Check to see if the outlet is wired backwards. It's cheap and easy to use. It is possible that your old house was also wired off.