Glenn, have you considered the RF switching frequencies generated in common household LED lighting? ChatGPT tells me that these frequencies can run from 20 kHz up to 1 MHz or even 3 MHz:Typical switching frequency ranges:
20 kHz – 60 kHz (older or very low-cost drivers)
60 kHz – 150 kHz (very common)
150 kHz – 1 MHz (higher-quality or compact designs)
Some specialized designs: up to ~2–3 MHz
If the bulbs are poorly filtered (seems likely) then such RF carriers could go directly into the household AC lines.
This wouldn't explain why all your different frequencies are going on and off at the same time, but it's another potential source of RF carriers in the LW spectrum. Now that I think about it, maybe these are the "most squirrely" LW carriers I often hear - and ranted about in a recent post.
73, Bruce WA1HGJ