Yep thats very common as you are drifting into sleep. My observation is the wired noises that you here and often people talking like groups of people is your dreamworld. You have Audio of this but not Visulization at that moment. At that moment you are in a transistion from the real world into the dreamworld. inbetween 2 levels. I can never get used to that when it happens to me because it always catch me off guard. But its very common. Usually people who are sensitive to these particular scenerios can become great WILD'ers