I don't want to count my chickens before they're hatched, but I haven't experienced the 80/40M noise problem since a few days ago. Maybe it's gone?
Interestingly, the same day that I stopped hearing the noise, I visited my neighbors and checked in with them about any RFI they'd been experiencing (their living room is about 40 feet from my G5RV). I'd operated in the NAQP SSB contest the day before, and they noted that they'd heard some RFI coming out of their subwoofer ("it sort of sounded like Vietnamese").
I explained that I'd been operating using a different transmission mode called single-sideband, and that the sound they'd heard was probably me. I also explained that there were some things they could do to eliminate the problem, especially reducing gthe length of cable going to the subwoofer, using some sort of twisted-pair cabling, and using some special devices (RF chokes) to eliminate the interference. I gave this speech a bit half-heartedly, since they're renting while their house is being renovated, so they'll be moving out in a few weeks anyway.
Now, these are really nice people, and have been great neighbors, so I decided to mention to RFI coming from(I think) their garage - who knows who's going to move in next? And if the noise-generating device is part of the rental, now would be a good time to figure out where it is so I can contact the property owner about fixing the problem.
The reaction was very positive; I was invited to look around, inside and out, and I looked for possible RFI sources. While walking around, I described the problem I was having, the hours I heard the problem (about 1600-2300 local time) and made a point of explaining that I could hardly hear anything on my radio while the noise was happening.
I didn't see anything obvious, so I explained that, if the subwoofer RFI was a problem, I'd solved a similar problem with my son's stereo, and I'd be happy to advise them on a solution, but more likely, it wouldn't be much of a problem before they moved back into their remodeled house.
Now, a week later, I've not heard any significant noise problems on 80 or 40 in the evening hours. Last week, I had a very pleasant experience operating in the CQWW 160 CW contest. And tonight, when I tuned around 160, 80, and 40M, the highest noise level I saw was S4-S5.
It could be a coincidence, but I suspect my talk caused my neighbors to turn off some piece of electronic equipment that was radiating noise. I need to check in again and see if this is the case (and thank them!).