Good so far.
Different home, different electrical circuitry. Ground loop hum is high on the list, assuming no physical malfunctions from cables, speaker wires, and such that might be causing a short.
When I've diagnosed hums in the past, by far the easiest procedure was to eliminate everything by disconnecting everything and building the system one component at a time. If that were my system, I would disconnect all the input and output cables from the preamp except the one going to the subwoofer. If hum remains, then plug the sub power cable into the same outlet as the preamp.
It is much easier to start with nothing and build than it is to start with everything and remove.
The most common source of hum in my experience has been the cable tv coax.
The second most common source I've had is from electrical outlets, including two outlets on the same circuit but separated by some distance.
This stuff can get pretty weird.