My 12-year-old home is on public water. Recently I've noted a pulsing noise at the supply entrance in the basement. Unless there is water flowing in the house, there is a distinct thrumming sound (about 40-60 pulses per minute) that can be heard and felt in the pipe. It stops if the valve before the meter is shut, but persists even if the valve after the meter is shut. If both valves are open and water is being drawn in the house the noise stops. I've had the municipal technician and my own plumber look at the problem (separately); neither has suggested a cause that explains these symptoms. I guess the next step is to have my plumber do a pressure test with the supply cutoff at the street to verify that the supply line doesn't leak. However, even if there was a supply line leak, I can't see how that would cause a periodic thrumming that would stop when the valve just before the meter is closed. Any ideas on what the cause could be?