I was woken up by a "tapping" sound coming from inside my wall. It sounds like water drips hitting something from high up. When I heard it, we had not run any water for about 2 hours or so (the last toilet flush before going to bed). It is inconsistent (I can hear 3 taps in a row and none for about 30 seconds then hear 2 more, so on). It seemed to stop all together for about 20 min then started back up. We live in a 2 story condo with finished basement and have lived here for about 1 year. I have never noticed this before (and I tend to notice these things). A Manablock system was installed before we moved in and all our drains (that I can see) are PVC. I do not see any water stains but don't want to wait for one to show up, either. Our main drain stack comes down through the wall between our kitchen and living room, but the sound isn't the loudest there. It is loudest in in area of our kitchen where no water or drain lines are (at least I don't think there are any there). But, I can hear it from almost anywhere in the house, which is weird. I wouldn't think a small leak could produce a sound I could hear almost anywhere.It is not an overly cold evening here (lower 50's tonight) and we have not run any hot water, so I don't think it is expansion of the pipes or anything like that. Any thoughts? I would not like to rush to calling a plumber or anything if not needed.

Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Good luck and thank you for rating my answer. Tom