Horrible hum issue in new practice space

[lunarpollen]

We have previously practiced out of the founding member's home, but I have just moved into a nice house where our singer lives, and the intention was to convert the upstairs loft area into a practice space (it's carpeted and has open walls on two sides and an open-beam vaulted ceiling, so the overall resonance is much less). Due to various things going on, we haven't yet held a practice there. But most of our gear is up there, and our singer and I have both jammed out on our instruments a bunch of times. And a major RF(?) hum issue has been discovered.

Sure, it is only a major issue with single-coil pickups, and if you are only using one of them. But the hum is very severe, especially with any amount of overdrive switched on, unless you turn to align the instrument on a very narrow axis (roughly north-south) and stand still.

I've tested the outlets up there, and everything is wired correctly. I've tried turning off all the fluorescent lights (no effect at all). I've tried unplugging the coaxial cable from the back of the television downstairs in case there was some kind of shared ground issue (no effect at all). I've turned off all lighting fixtures in the house that are on dimmer switches (no effect at all).

I'm guessing that it's some kind of wiring issue in the house, but it's not something I can fix (I'm not an electrician). Is there anything else that anyone might be able to suggest to help alleviate if not eliminate the problem? Otherwise, for songs where any of us is using just one single-coil pickup, we will just have to align ourselves to the most hum free direction and not move at all.