Mystified in Chicago (Pipe Noise)

[watts28]

Can anyone help me with this strange question?

In the past 5 weeks I have noticed a pipe "banging" sound (not exceptionally loud) once water is running within the house. I would say it takes 2 - 3 minutes to start and continues with a "bang" every minute or so. If the water in the house is shut off, the "banging" will continue at the same rate for about 10 minutes. I've heard water hammer before, but why would it continue for so long after everything is shutoff? I shutoff water to the house and allowed the system to vent, but this did not eliminate the issue.

Does this sound like a drain issue or a supply issue? If its drain related, should I attempt to see if the vent stack has an obstruction?

Thanks for your help.

[hj]

"Water hammer" does not occur while you are running the water. It occurs when you shut the faucet off too quickly, and even then it is a momentary thing. Under certain specific conditions you can get water hammer when you open a faucet too quickly, but it is a rare situation and requires very specific parameters for it to occur. In either case the hammer only occurs for a fraction of a second and then disappears. You have some other condition, but without being there to hear it and test all the possible causes we cannot help you solve it.

[watts28]

HJ

Thanks for your input. This seems quite unusual. I plan to shut off my water supply and then pour water down my drain to see if the noise still occurs. Perhaps this will tell me if it is supply line related or not.

After that, its a call to the plumbing authorities!

[jadnashua]

Does this happen when running cold water, or only when running hot? If hot, it could just be either the supply line or the drain expanding. Then, after you stop, as it cools, it contracts. If the pipe(s) in question have a tight fit through a wall, floor, or stud in any way, that could be it. Actually, it doesn't necessarily have to be rubbing on something, it could just be expanding/contracting, but it usually makes more if it is rubbing on something. My unprofessional opinion.

[watts28]

jadnashua -

That's a great point! Thermal expansion sounds like it could be it since it continues for awhile after shutoff. I'll check out the hot / cold question.

I appreciate your help.