Just read your reply about it being excess moisture in the air. Our bathroom is small, and is on the 2nd floor. It is winter, so is pretty dry in the house, although obviously not so much in the bath. Would it still be the same thing? It only just started a week or 2 ago...we've been here for 2.5 years.
Also...how do you stop a running toilet? Juggling the handle isn't working.