Check all your toilets for a leak in the flush valve (flapper valve) by opening the toilet tank and adding food coloring to the tank, but don't flush the toilet for an hour or two, and look into the bowl to see if the colored water leaks from the tank to the bowl through the valve. If so, the water level drains down at night so slowly that the fill valve tries to open and close so quickly that it vibrates, and the occillation causes a moaning sound. Sometimes the moaning comes from the ice maker in the refrigerator, and occasionally the washing machine electronic fill solenoid, but usually its the toilet.
: For the last week we've been kept awake by a loud moaning in the pipes. We live in a 4-story condo building and at first we thought it was a plumbing problem. We checked with both neighbors above us and they assured us they were not having any problems with their plumbing. One neighbor, a former building contractor, said the moaning noise sounded like air. He said it might be air coming through an uncapped pipe in the roof or air coming from a sewer line pipe.
: We would appreciate any advice you might be able to offer. The moaning is keeping us awake at night and driving us crazy.
: Thank you.
: Carol Greenspan