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I live in a condo...upstairs with another unit behind me with the plumbing in the shared wall between us. Whenever it's been awhile (say 45 minutes to an hour) since any cold water has been used, if I flush either of 2 toilets or run any cold water faucet, I hear a dripping sound that is loudest in the wall of the kitchen.

It starts about 15 seconds after the water starts (flush or open faucet), drips (tapping sound) very quickly and then slows down and stops. After that, I won't hear it again until the water has been sitting unused for awhile. It's only cold water. The only thing I hear when hot water is used, is the slight knocking from heat expansion after it's running for 30 sec. (it's winter).

There is no apparent water leak upstairs in the kitchen or downstairs in another unit. This just started about 6 weeks ago. It's almost as if water is accumulating somewhere in the pipe and using the water pushes this accumulation out of the way.

I don't know if it has any bearing (or just coincidence that it started around the same time), but I believe the vent to the roof has something blocking it, as my toilet water levels (especially 1 toilet) go down at varying rates. Sometimes I'll come home and find a tiny little something that backed up into the toilets. A plumber has already checked for a toilet leak and it's all dry. I'm waiting for the Spring until someone goes up onto the roof to check that out.

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Are you sure it's really water dripping and not thermal contraction from colder below grade water running into the relatively warmer pipes in the wall? That is my best guess. While it's possible you could be hearing sink drains dripping, (the availability of proper venting would not affect this one way or the other) toilet drains dripping would more likely be heard by your downstairs neighbors, not you. – bcworkz Feb 27 '13 at 1:05
It's definitely tapping and only from cold water running (filling toilet after flush or turning on cold water faucet). Starts out quickly, slows down, then stops. It's not the toilet drain...that goes downward & not over to kitchen, where it's heard. Hot water running only causes light knocking from expansion...no tapping. This is ONLY cold water. If I don't wait as long (1/2 hr) I get a slow tap...like water has not had as much time to accumulate. – user11786 Feb 27 '13 at 7:34

I was reading the explanation provided here:


I have the same problem and agree with most likely the fact that is expansion of pipes.

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-1 for link based answer. Links tend to go bad over time. – BMitch Jan 7 '14 at 12:48

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