We have begun to hear a humming sound in the plumbing. Its been happening a few days now. When the water is running (up or down stairs) the humming will stop. It starts up again when the water is turned off. The humming can last a few minutes or almost an hour. Then it stops. Is there something I can do to stop or fix this or is calling a plumber in order?

See if you have any backflow adapters on your outside hoses. They hum when leaking. Also check the main pressure reducing valve on the house. When they are going bad they hum. Also need to check for leaks in toilet flapper valves.