It is continuously making a sound and at some intervals, it some of them might even play a little tune. It is not distractingly there when there are other environmental sounds, though it is there if you disconnect yourself from the other sounds and also there when there is no other sounds in the environment. Some of them are quite shy to darkness, where they don't play their little tune at some intervals, otherwise it will be abrupt in the light and become noticeable. The sound by itself will be in sync with time itself, though when next to another of itself, it will always be out of sync with each other. It is actually the mechanisms of the object that produces the sounds which comes in different sizes to produce higher pitches or lower pitches. Everyone experiences this sound differently, for some people it will be fast and others slow though in reality it always making sounds at the same speed.