I just moved in to an 8-year old 3-floor townhouse. I noticed the dripping water sound in the wasll after showering. The sound is very clear in the third floor, and dims a little in the second and almost gone away in the first floor. The sound keeps for a while and then disappears. I could not find any sign of leaking on floor, or ceiling or wall. Last night, things become more weird, at midnight I was waken up by the dripping sound while no one is using or just used the shower. What should I do? Use a snake or chemical cleaner? Call some handy man to take a look? Thanks a lot.

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. Regards, Tom