A loud click or snapping noise

     Since we moved into this house,  in the summer of 1979,  we have experienced an unusual loud noise in the master bedroom. I cannot say for certain that it occurs every night because we often turn in after 11:30  and the sound usually occurs sometime after 11 but before 11:30. It sounds like a loud snap  which usually repeats, slightly less loudly, a few minutes later. The sound appears to come from the southwesternmost corner of the room where a dumbwaiter used to be located. The dumbwaiter was taken out of service and walled off sometime in the late 1940s. But if we chance to turn in a bit early, we about always hear this snap or click. The dogs do not appear to take notice of it. I tend to think it has something to do with temperature change in the old sealed dumbwaiter shaft. But precisely what????? I have no idea. Nor why the noise is always in that short time window.