We purchase our 7.5 yr. old home four months ago; after moving in, I noticed a "ticking" sound in the water closet (separate toilet). At first I thought it was a drip behind a wall. I have narrowed it to a ticking noise (very intermittent) above the vent/light kit. I have a bathroom above it and shut all water off to it with no change (still ticking). I can't get the housing for the vent out now, but can hear the noise. Anybody have a clue as to what it could be???