Periodically my the pipes very close to the hot water heater will start to bang very loudy. They will bang for approx 20 seconds every few minutes for anywhere from 5 min to an hour before subsiding. Turning on any facuet in the house will make it cease. We live in a tri level home wth the hot water heater at the bottom of the house and it usually starts when a tolit is flushed upstairs (or a bath is run). On a side note... there is usually one bang noise that occurs when our outside sprinklers come on... but it does not bang continuoulsly. Just a side note in case there are related. Any help would be greatly apreciated.