Hi there.

Our house was built in 1990, and we've lived here two years. When the hot (not cold) water drains, there is a persistent knocking (about 1 knock every 1-2 seconds) in the pipes that can be heard from anywhere in the house (2 stories and basement). If you fill up a sink with hot water, no noise. When you drain the sink, the pipes knock. This occurs regardless of season (e.g. winter versus summer) and in all locations of the house - e.g. bathrooms (sink, bath, showers), kitchen (sinks & dishwasher), & laundry room.

Can you give me some ideas re potential sources of this problem, whether this is a problem versus a nuisance, and what might be involved (work and $$) to repair?

Many thanks!

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 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 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

Good answer Tom identifying Thermal expansion in drains...

The original plumber drilled holes for drain pipes too tight. I doubt shims will solve it. You would have to open every stud penetration and shim it. It sounds kind of impossible to accomplish w/o tearing up whole house. I will go with your second suggestion: learn to live with it...

Yeah Milo, When folks learn how much of a hassle and expense it will be to track it down and repair, it then becomes a conversion piece. " Oh Look Honey! The walls are talking to us again." Cheers, Tom

Yeah Milo, When folks learn how much of a hassle and expense it will be to track it down and repair, it then becomes a conversion piece. " Oh Look Honey! The walls are talking to us again." Cheers, Tom


Thanks for your speedy and helpful answers. The sound does appear to be isolated to a particular wall that's only about 6ft in width - it's the wall to which all the pipes eventually flow. Does that make a difference either in the feasibility or cost of fixing the problem?

Thanks for your speedy and helpful answers. The sound does appear to be isolated to a particular wall that's only about 6ft in width - it's the wall to which all the pipes eventually flow. Does that make a difference either in the feasibility or cost of fixing the problem?
You just made it easier! It directs you to one six foot section of the wall. This pinpoints the source of the noise. All that remains is to open up the wall and shim out the noisy pipe or pipes.
Good luck, Tom