My pipes have been "singing" lately, especially during the hottest days. Everything outlet (kitchen sink, dishwasher, toilet, lavatory, shower) in the house causes the sound. It occurs mainly with the hot water, but the cold cause it intermittenly Over the weekend we found that the sound travels all the way to the meter.

From my research, I thought there might be a bad washer in a faucet, but since all the outlet cause the sound it makes me fear that it might be something worse.