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Old 01-15-2014, 01:01 PM   #1
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Loud dripping sound heard while draining the sink


I noticed recently sometimes if someone is draining water from second floor bathroom sink, I can hear loud dripping (or knocking) sound downstairs. The sound went away in 30 sec. I first thought something is vibrating downstairs, but later on I confirm the sound is from above the ceiling. I monitored the ceiling for a couple of weeks, and haven't noticed any water leak. Has anyone experienced this before? Thanks.

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Old 01-15-2014, 01:36 PM   #2
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Loud dripping sound heard while draining the sink


PVC drains can be noisy----so unless you see a leak--it's likely just water in the drains.

Some really high end homes still use cast iron drains because they are quieter.

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Old 01-15-2014, 02:22 PM   #3
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Loud dripping sound heard while draining the sink


May also be pipe rubbing on wood due to hot water expanding the pipe. Hard to locate sometimes
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Old 01-15-2014, 02:29 PM   #4
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Loud dripping sound heard while draining the sink


It is like something is vibrating vigorously. The first time, I thought about the cups in the cabinet were shaken by the earthquake. But I am in new england, supposely no big earthquake.
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Old 01-15-2014, 02:38 PM   #5
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Loud dripping sound heard while draining the sink


Could be the water lines vibrating. More commonly referred to as water hammer. It's not uncommon for water pipes to next to a drain line. Is it noticeable when the faucet is on or slightly open?
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Old 01-15-2014, 02:39 PM   #6
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Loud dripping sound heard while draining the sink


The faucet is off. It only happens when draining the water.
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Old 01-15-2014, 05:41 PM   #7
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Loud dripping sound heard while draining the sink


I've got this too, in my bathroom sink drain. I've learned to ignore it. Running hot water down the drain results in a pretty distinct knocking/tapping sound coming from the wall. It's just the PVC pipes expanding and rubbing as they heat up.

If you get different results testing with different water temperatures, then I'd say you've got the same issue going on.
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Old 01-17-2014, 07:56 AM   #8
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Loud dripping sound heard while draining the sink


I did some tests at home last night. With the same sink, I was upstairs, and my wife was downstairs. I first started with running cold water. No noise. Collected enough cold water and drained it, no noise. Running hot water, the noise appeared in about 15 sec. I can hear it hehind the wall on the second floor, and my wife heard it above the ceiling. It is loud, fast, high frequent knocking/tapping sound. Turned off faucet, the frequent noise stopped immediately. But in the next 5 min, you still can hear knocking sound every 15 sec or so until it completely went away.

So it might be air in the pipe or thermal expansion. What can I do?
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Old 01-17-2014, 12:20 PM   #9
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Loud dripping sound heard while draining the sink


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Originally Posted by shiyang100 View Post
Running hot water, the noise appeared in about 15 sec. I can hear it hehind the wall on the second floor, and my wife heard it above the ceiling. It is loud, fast, high frequent knocking/tapping sound. Turned off faucet, the frequent noise stopped immediately. But in the next 5 min, you still can hear knocking sound every 15 sec or so until it completely went away.

So it might be air in the pipe or thermal expansion. What can I do?
IMO, what your hearing, as others have mentioned, is the normal thermal expansion of the pipe warming up and cooling down. You also have the wood the pipe is traveling through and the brackets securing the pipe expanding and contracting, which is contributing to the noise as well.

I'm not sure how to fix it, I would suggest pipe hangers, supports that have rubber cushions and drilling a bigger hole for the pipe that's traveling through the floor/ceiling. The pipe that's running through the floor and ceiling may be too tight with not enough room for expansion. Not sure how this could be accomplished or if it's even practical without removing drywall, etc. Sorry I couldn't be of more help to you. Stay tuned, let's see what others reccommend. Thanks.

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Old 01-17-2014, 12:42 PM   #10
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Loud dripping sound heard while draining the sink


Thanks JMon. We moved into this new house six years ago, and haven't had this problem until a couple months ago. That's why I hesitate to believe it is pipe expansion. Otherwise, it should be there since the beginning.
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Old 01-17-2014, 01:03 PM   #11
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Loud dripping sound heard while draining the sink


I agree. After you have investigated it a little further now, you appear to have some other issue going on affecting just your hot water line.

Just curious, probably has nothing to do with it, but whats your incoming water pressure set at? Can be checked at a hose bib or sink.

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Old 01-17-2014, 01:10 PM   #12
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Loud dripping sound heard while draining the sink


But I just couldn't figure out what other possibilities are. Are there any other tests I should do?
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Old 01-17-2014, 01:20 PM   #13
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Loud dripping sound heard while draining the sink


Whats your incoming water pressue set at? Can be checked at a hose bib or sink.
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Old 01-17-2014, 01:31 PM   #14
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Loud dripping sound heard while draining the sink


I will check it out this weekend. But I only have the problem with one upstairs bathroom sink. Do you think water pressure still might be the cause?
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Old 01-17-2014, 01:49 PM   #15
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Loud dripping sound heard while draining the sink


Probably not. But then we can rule it out for sure. Thanks.

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