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.