Search:

From speedball1:
The problem is caused by the ballcock trying to fill while water is seeping out of the tank. The sound you hear is the washer vibrating against the seat of the ballcock. First check...

A transformer out on the street?

It sounds like a transformer. It could be a meter. It could be in your house, unless you really turned off the main breaker electric.
My house has 2 transformers next to the circuit panel that hum...