# Rhythmic knocking



## bilghali (Mar 2, 2009)

I have repetitive rhythmic knocking (like morse code) in the main cold water supply pipe to the house. The sound ceases when the water is running. I can feel the knocking in the water meter which stops the sound when fully shut.  Any Ideas?


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## glennjanie (Mar 2, 2009)

Welcome Bilghali:
Some water meters make that sound when they are measuring the amount of water used. Is the needle moving on the meter at all when you have the water off? If it is, you have a water leak.
Glenn


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## jdougn (Mar 4, 2009)

Hello Bilghali,

How loud is the knocking? It may be a harmonic rythm from water pressure. This is more common in boiler based hot water heating systems but may also be causing your knocking. A plumber would install a 12" riser, a vertical section of water pipe, close to the first right angle turn in the main line. The 12" riser would be capped so that it holds air. The air dampens the knocking.
hth, Doug


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## handyguys (Mar 5, 2009)

My experience is it makes the knocking when running water and no noise when not running water. I have noticed that when running lots of water at once that the knocking may stop being as obvious or it just changes pitch/frequency.

Check it when you are SURE no water is being used.

If it knocks when you are positive no water is running (toilets may be culpret). Then check for leaks or a neighbor running a hose to his house to save on his water bill. (seen it)


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