Strange pumping sound still eludes discovery

 Last Sunday the pumping-like sound occurred at 4:01pm,6:01pm,7:01pm,9:01pm,10:01pm,11:01pm. Each time the sound was repeated 6 or seven times. Plenty loud enough to hear in the Library but no where else inside or outside of the house. On Monday the sounds were heard at 9:02pm, 10:02pm followed by a single kerthump at 10:12pm, then back to normal at 11:02pm. Today (Tuesday) the sound started at 3:02 in the afternoon, but was not heard again until 6:02pm. I await, yet, the 7:02  which is 10 minutes away as yet. Not knowing the source of this noise is very frustrating. Not knowing why it is audible in only one room is mystifying.