I recently had a similar problem with water running for hours through pipes in my ceiling and wondered why a tap would be left running. I found it to be a faulty toilet in the apartment above. When the toilet was flushed water would continously run through the toilet and then the pipes in my bathroom ceiling. A simple fix of the toilet valve above and no more water running. Another apartment needed washer changes in their taps. I believe that was causing hammering in my building, not sure how true that info from my plumber is though.
Cheers,
CBF