I woke up at 3:15 because something beeped, once. I woke up an hour later because something beeped again. I felt like I was in the thread
Mysterious Beeping in House - Help! - TiVo Community (warning: the thread in question is presently 2213 posts long, but there is an answer in there somewhere).
I hope to find the source of the beep before I go to sleep tonight.