I too have a faint dripping noise that I hear coming from back of toilet. Now, on the floor below, also a bathroom, we are having the ceiling replaced and the pipes are exposed. One night I heard a drip, drip etc., so I stood under the pipe and that's when I really heard it. It doesn't appear to be leaking from said pipe though. Afraid to finish ceiling while this is going on. I put a color tab in the upstairs toilet but it doesn't color the bowl water. Help! It's driving me crazy. Should I just call a plumber or what?