Agree with John D. Is it a bathroom with roof directly above?
Had similar in my old house, turned out to be water getting into the fitting from a small break in the slate of the roof. sorted that out and problem was solved.
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local