I found one of my sources of interference. I have an E-Wave detector from HobbyBoards that would go off every day about 8am, and I couldn't figure out why. Then, setting up my Blitzortung H-Wave, I'd see the same interference at the same time. This morning, I was getting tons of signals (8-40 a second), and started looking around. Everything was in the 10kHz range. Opened up the door and heard the school next door giving a fairly long PA announcement. Every time the speaker would stop and clear the mike, the signal would stop, then would start back up the moment he would start speaking. The bells don't seem to set off the detectors, just the announcements. Attached is one of the waveforms I am seeing.
Argh! Luckily, it only goes of predictably every morning, so I can set up a cron job to disable sending at 7:55am and re-enable it about 8:30am.