After finally mucking with it enough I managed to get MythTV behaving. I found my antenna lead was loose, which may have caused random static in the picture. I also moved the antenna a few degrees away from the direction it was pointing. The combination of the two may have been enough, though I’d like to find out which one made the difference.
I also reinstalled the Myth database the other night, deciding to wipe it clean and start over. I don’t think this could’ve made a huge difference but it was a good exercise anyway. I had to do something with it because when I consolidated my Maestro server with my MythTV server the name of my Myth box changed. When this happens, Myth gets Very Unhappy, requiring some manual database trickery to get it going again. I think my trickery may have left me with an unstable database, thus the need for a reinstall.
Now to add in all the shows I had once set to record.