Strange pumping or thumping sound returns

   I'm not surprised that the strange sound has returned, but where it has returned. The sound is no longer heard in the Library. Night before last, the thumping sound was heard, very loud, in the kitchen by me. My wife was on the computer in the library and heard nothing. The thumping went on for a good 10 seconds or more. I was taken totally by suprise because before it was heard only in the Library. I moved in the direction of the sounds apparent source but the moment I stepped from the kitchen into the short hall that connects to the dinningroom, the sound stopped. Last night, again I was in the kitchen when it sounded. Again it was louder than it ever was in the library, but lasted only 5 thumps. My wife was in the dinningroom and again heard nothing. We were out all day today so I don't know if it continued to sound or not. But the sound, to me, is loud enough that it should be heard all over the downstairs....but it isn't. Weird. Actually, this time the thumping sounded very much like someone driving a metal post into the ground with a sledgehammer. None of my neighbors work outside after dark and besides why is it only heard, now, in the kitchen?