Drip in Wall?

[Micp879]

Hey Guys,
First off, I want to say thanks to Terry for this forum. Because of what I have learned here, I was able to repair a leaking toilet and save myself the cost of having a plumber come out to do a simple fix.
Second of all, I have a question for Terry and any other knowledeable plumbers out there. I bought a brand new 3 level townhouse 4 years ago. It was a new development, so there was noone living in the home prior to me. My problem is in the half bath, which is located on the middle floor. For the last 2 or 3 years, I have noticed an intermittent sound coming from the wall behind the sink. After I use the sink for the first time that day, I hear a loud dripping or tapping noise coming from the wall behind the sink. It only happens after using that sink, it doesn't just happen when no one is in the bathroom. Even when that sink is used, the sound is very sporadic. Sometimes I wont hear it for months, other times I will hear it every day for a few days, and then I wont hear it at all for a few days. If I immediately turn the water back on and shut it off again, I normally don't hear the sound again. I have filled the sink with water, and then pulled the plug to let it empty out, and I typically don't hear the tapping/leaking noise. Is there any idea what this could be? Im afrad its a leak in the wall, but I dont want to tear into my wall if its not an actual leak. Ive checked the floor around the sink, as well as the ceiling thats directly below the bathroom, and there is no sign of water damage. Ive had people tell me anything from a leak in the wall, to water leaking inside the pipes, to it just being the pipes creaking as water moves through them. Any thoughts or advice is greatly appreciated. Thanks in advance. Keith

 

[Prashster]

I'm no pro...

But, those dripping sounds might be the sound of the drain pipe expanding and contracting and rubbing against a framing member.

The fact that it happens early in the morning supports this theory.

Do you notice a difference in the sound based on whether you're running hot or cold water through the drain?

Does the sound vary based on the outside temperature or humidity? I'm not talking about a scientific measurement here; but does the sound change/go away when the seasons change?

If it were really a leak, I'd think you'd SEE it on the ceiling below before you'd hear it behind yr sink. Any drips from a leak would likely fall on the ceiling board or wood - not hollow pipe (which is the only way you'd hear it).

 

[Sponsor]

 

[hj]

drip

It is an expansion noise and the frequency depends on how fast you are running the water. If you have a slow flow it could happen so slowly that it doesn't make the noise. It also makes the noise when the pipe cools, but it happens so slowly, that you either do not notice it or it is so quiet that you cannot hear it.

 

[Geniescience]

to help you convince yourself as to what it is most likely to be, you can isolate the variables.

Draw water from the taps in advance, store it in spare containers, and use that water first thing in the morning. You will see if putting water into the drains does or doesn't cause the noise.

Then, turn on the water and see whether the noise starts. You can run a lot of water, as this will cause the most expansion or contraction in the pipes. If you hear a noise then, it'll mean that the noise is due to the supply pipes. So then it's either a leak (drip drip noise) or an expansion causing a (snap snap snap) on some days (and just rubbing quietly on other days).

Do you have any other pipes in the same wall going upstairs? Are there other pipes directly above ?

David

 

[Micp879]

Prashster, actually yes, it does seem to sometimes vary by the season. During certain parts of the year, I wont hear the noise for a few months.

Genie, I dont believe there is any other piping above it, as the area above the bathroom is just a walk in closet.

 

[Mikey]

I'm with HJ, and would add that it's most likely a supply line, and probably the hot-water line that's making the noise. You'll notice it most on a cold morning -- the pipes have cooled (and contracted) overnight, and when the hot water for shaving runs through them they will expand, rub on the building structure somewhere, and make that tapping sound as the static friction is overcome and the pipe moves. Down here, occasionally the opposite happens -- the pipes warm up (and expand) during the day, and running the cold water will cool the pipe and make it contract. I've got CPVC running in the attic the length of the house (about 100') and the maximum difference in the pipe length is something like 2 or 3 inches -- I forget the exact figure, but it's a LOT more than I would have guessed.

 

[Micp879]

Thanks everyone thus far for all your input. Im hoping it is just the pipes contracting that I am hearing. I really don't feel like having to knock out by bathroom wall if I can avoid it lol. If anyone else has any thoughts or opinions, feel free to throw them my way.