This just started happening recently... after using the water (sink or bath) in one of our bathroom, there is a single knocking sound that occurs every 10 - 15 minutes or so for the next hour to hour and a half... then it stops until the next time someone uses the water in that bathroom. Any idea what is causing this? Loose pipe perhaps?? Thanks.

Henry

Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Regards, Tom

Thanks for you reply. I could live with it... I guess I was mostly concern about whether there could be any long term problem with a leak developing.