Unexplained pumping or thumping sound

    The unexplainable thumping sound that sounded on such a regular hourly basis in the library has not been heard in the library in weeks. Now it sounds off on very irregular periods in the kitchen. Louder than it was in the library, it is the same noise, only louder. Even though it is louder it is not heard in any other room. Just as it was not heard anyplace else when experienced in the library. The library sound was heard on schedule every hour on the hour. The sound in the kitchen is not regular. It sounds and may not sound again for a few days. Other than not being able to figure what causes it, its not a problem; but can drive you nuts trying to figure out its origin.