Strange sound is daily now.

     The inexplicable pumping sound which can only be heard in the library and nowhere else in the house or out of the house; has been occuring on a regular hourly basis since I last posted about it here. The sound does occur on rare occassion in the morning, but is most reliably noted between 6 and midnight. Sometimes its louder than other times. Sometimes its more rapid than at other times. It only lasts 5 or 10 seconds at a time.Its never exactly the same time of the day, but it is pretty much exactly one hour to the minute each day. If its heard at 6:54 you can set your watch you'll hear it again at 7:54 and so on. But the next day you might hear it  at 7:53 and so on. Some days (rare recently) you don't hear it at all. I suppose it has a logical explaination. But only hearing it in one room and not being able to source it out is becoming a real problem.