I noticed an odd noise coming from our fixtures. It was loudest upstairs in the washing machine, which acted like an amplifier. Downstairs, I got the best result by attaching a mic directly to the incoming water line with spring clamp. That is the pipe recording. 

It turned out this could have been used as an early diagnosis method for the water main break, which took another day to show up as above-ground water at the street. The sound was the turbulence of the water as it escaped the pipe, and presumably rocks and other objects banging against the side as they swirled around.

Pipenoise - On Pipe - Lowpass

meesterx