I've had this happen when I'm going to sleep as well which usually makes my leg go rather stiff usually causing me to straighten it out or something. To this day still not to sure what it is, but I would hedge a bit on probably something from the mind and what it's trying to do, but as to the goal that I have not figured out yet.
P.S. About the noise perhaps it's merely your ears becoming more in-tune to the electrical currents that are flowing within' the room. I only say this because it's happened to me quite often, but it is not the end all answer for everything as I've come to figure out
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