During the night we are woken by a loud humming noise which goes through the whole house. When we turn on the taps the noise stops, but as soon as the taps are turned off the noise starts again. The only remedy that we have found is to turn off the cold water at the main stop cock inside the house. This is left off for the remainder of the night. When turned on again the humming has stopped.
Strangely to us this sometimes happens during the day, and just running the taps cures the problem.