Heard a loud, mysterious whine in the bathroom next to my home office.
Audible in the basement, too, loudest under the bathroom. One by one,
turned off each of my 32 breakers. The whine disappeared when I tried
the 30th--which made no sense, because it controlled the kitchen, at
the other end of the house; and then it re-started before I even
flicked the breaker back. Finally got smart and checked the outside
valve for the garden hose. It was turned on, and leaking slightly
around the valvestem, while the hose was shut off by its spring-loaded
nozzle. Turned the valve off and the whine stopped. Lesson: Not all
electrical-sounding whines are electrical.