Our new home that we built started humming after an AC adjustment. It is low ptched and intermittent and drives me crazy. My husband cannot hear it and like rattling autos, it won't hum when someone is here who can hear well. We moved in 10 months ago and this is new. I hear it at night when other ambient noise is low. It pulses on/off and at times it aggressively bumps on and off. We have a hot water circulation system, HVAC, in floor heat, security, TV, and solar hot water panels and about 4K of photo voltaic panels for electricity. We also have some high tension lines in view but they never caused a problem the first 10 months of occupancy. Any ideas?

I would Turn all breakers off 1 by 1, maybe shut off water valves to determine the culprit.

I too have experienced a low frequency hum throughout my house. It was driving me nuts. My wife couldn't hear it, only me. I traced it down to my vent stack pipes on my roof. I put a couple of 90 degree elbows on each vent to turn the outlet toward the roof. The low droning hum went away. I'm not saying that this will fix the problem that you are having but, you might give it a try.