It is not surprising that supersition should have its own explanations for the errie knocking sounds often heard in old buildings that more rational modern minds might attribute to insects or changes in temperature. An old but still familiar tradition speaks of the three knocks of death that are heard to rap at the door, at the window, car, or even at head of the sickbed when the occupant is about to expire, and many people still become nervous when they hear the knocking noise emitted by the death-watch-beetle as it calls to its mate, claiming that this is a warning of the presence of death.
A US traditon recorded in Viriginia places an ominious significance upon no one answering the door after a caller has rapped on it, and concludes that this is yet another omen of imminent demise.
In some cultures it is also believed that the knocking sounds are emitted from spirits trying to gain attention, or that three knocks together could mean a demon in your presence.