Just spoke with the neighbor, and I let her know of the problem. I gave her the roughest estimate of where in her house the problem is (Dead center from side-side, and about 10 ft from the front of the house).

She asked me what to do, and I offered to hunt down the source in their house, but she wasn't very receptive (I even offered the opinion that it sounds like something is arcing, which is problematic for more than one reason to her and her husband). At which point, I left it at that, and offered to help hunt it down in the future when she contacts an electrician.

Not sure where to go from here. I don't want to alienate a neighbor, but I'd also like to work HF... Maybe re-orienting the antenna is just the best way to go, to try and null out their house?