ka9q

I'm listening to your SDR now but I don't hear it, probably because it's too late (0108 UTC). In fact you have a remarkably quiet QTH compared to mine (San Diego CA DM12ju). But your description sounds remarkably like one source of QRM I'm working on here: clearly power line related, very unstable lines from a switching power supply, present after dark until the middle of the night, worst on the 49m and 40m bands (receiving with a G5RV).

The switching frequency appears around 20 kHz, i.e., the lines blanket the spectrum every 20 kHz. My hunch is a compact fluorescent bulb, as their switch mode ballasts produce 20 kHz AC where CFLs are most efficient.

As for the noise coming down your power line, yes, this is exactly what I'd expect. Electronic noise below about mid HF is generally conducted out through the power line since the device itself is too small to be an efficient radiator.

Have you offered to buy your neighbor a new, clean light bulb? That's what I plan to do once I find out who to offer it to.