Heh, I wasn't aware of Night Vale. Very interesting!

There is a vent fan in that room, but I know where the switch is and the fan is brand new. It's possible that the sound could be coming from it, but I'd be surprised...

I could try turning the breakers on and off, but I don't think that would tell me all that much about where it is. I already know that it has to be somewhat near that WC, but I don't know which direction. Like Tony's place, the breakers are mostly geographic and are extremely poorly labeled. I'm always shocked by how poorly most breaker boxes are labeled in this country. Most of mine just say something like "lghts & plgs," with no indication of WHERE those lights and plugs are located. I've also noticed from past experience of replacing wall switches that there is rarely a logic to which switches are on which breaker. For example, there are three breakers that cover all the light switches in our kitchen.

I think the next thing I'll try is to find a way into that space above the garage. I'm a little worried about what I might find up there. It's extremely difficult to get to, so I don't know if I want to risk my health to get up there, but we'll see. Thanks for your help so far, guys.