I found a way to stop the RFI coming from my TiVo on 80 meters: unplug the S-Video cable from it! Our TV is connected to the TiVo via the RCA cables, so the S-Video output wasn't being used. Unplugging it from the TiVo solved the problem.
If I actually were using the S-Video output, I would have needed to try to stop it from radiating, but this fix is a bit simpler!
So, if you're experiencing this kind of noise, it might be coming from the S-Video cabling.