continuing knocking sound in water pipe half an hour after all water off

This knocking pipe problem is really strange. It is a weak knocking sound 2 or 3 times per second normally happened at night time in about half an hour after all water usage is stopped. Once it started, it will keep knocking till the next morning. It really drives me crazy. The only way I found that can stop it temporarily is using water like flushing the toilet. It will stop the knocking about another half an hour. So imaging that, wake up by the noise at 1:00AM, flush the toilet, try to get back to sleep before 1:30AM, if not, flush again... Anyone can give some advice?
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Instead of wasting the water on a flush, take diuretics and make the flush do something.
Do you have shut off valves for each fixture? Try shutting off some of them, or a zone if a section must be shut down and see if that stops it or help locate the problem. My guess is that a toilet valve is not closing properly and while barely visible, is very loud. That would be the first place to check.
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On Jul 3, 2:30 pm, snipped-for-privacy@gmail.com wrote:

try shutting off the supply to the toilet
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wrote:

Yep. the toilet. The flapper has a slow leak which causes the water valve to turn on very slowly making all sorts of evil noises. Fix is to replace the flapper and while you have everything apart replace the fill valve also,
CHeck this by turning off the toilet water and see if the tank drops any over night
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Thanks for the advices. I turned the toilet water off last night. It seems work. I will retest it tonight to confirm it.

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kekil had written this in response to http://www.thestuccocompany.com/maintenance/Re-continuing-knocking-sound-in-water-pipe-half-an-hour-aft-230973-.htm : i know this was a long time ago .. but any update on this? wondering if it worked for you. me and two other people have the same issue!!
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On Tue, 03 Jul 2007 19:35:33 -0000, snipped-for-privacy@gmail.com wrote:

It's probably haunted. This is one of the undisclosed "features" of a Gmail account.
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