In my house, each breaker is geographic. The lights and the power outlets for a given section of the house are on the same breaker. So narrowing it down to one breaker might not help that particular thing.

But... narrowing it down to one breaker might certainly be of help. For instance the garage or attic might be on a different breaker than the bathroom. So if you kill the garage breaker and the noise stops, then there might be a chance you're hearing something from the garage filtering through.

Here's another question for Dignan:

You mentioned somewhere earlier that the section of the bathroom with the noise did not have a window. You had to leave that section to get to a window. Well, I'm pretty sure that WCs which don't have windows are required to have ventilation fans. Have you already narrowed down that it's not the vent fan for that room?

Most vent fans are activated by a switch. Where is the switch for the vent fan for that room? If you don't know, then, maybe there's a switch somewhere that's always been on and the noise will go away if you turn off the switch.

The noise certainly could be a vent fan turning on and off at regular intervals due to being old and flaky. I've seen fans that have gone bad which, even when turned on all the time, will spin up and spin down like that. If the fan blades were rubbing against something, they would make a rising and falling pitch, much like that sound.

Another suggestion: Does your house happen to be situated next to a dog park?