Electrical noise field radiating from the house

[Baxtercat]

outdoor transformer?

My old house in an old neighborhood has a perpetual house buzz too.
If I take an unplugged speaker - even an old telephone handpiece - around the house or backyard I can still hear the magnetism moving the coil faintly. I can't record at this location.

[Rhodesplyr]

To me, the phasing effect is a giveaway that the noise is ultimately coming from some SCR controlled appliance or other. The same kind of idea as a lamp dimmer, but it's getting ramped up and down for some other purpose.

Steve,

I think you win the diagnostic prize. I finally traced the mystery noise in the house wiring to....drum roll....an APC Back-UPS XS-900 battery-backup power supply for my computer. (I live in a neighborhood with a lot of old trees, and we often lose power in storms.) I imagine it must have an SCR or some other similar device in it that's malfunctioning, and it was using all the wiring as a broadcast antenna.

In the process of tracking this down, I've also lowered ambient noise by improving the house's grounding. Its grounding rod was sunk into a large brick planter, above grade (which you're not supposed to do), and the grounding rod itself was the galvanized type that's been found not to hold up well. I've driven two eight foot copper-clad rods into the natural soil twelve feet apart, which is the current recommended best practice for this area based on soil types.

After knocking out those two problems, the weird cyclical noise is gone and hum from sensitive electronics is greatly reduced overall.