I have gotten this too. I really think it is the same thing as the other twitches, just feels different because of the location. I would not worry about it as it has never hurt me, just drives you a little nuts. Muscle twitching anywhere is harmless and I got that answer from my Moms Neurologist.
Although the vibration/tingling/shaking/whatever is driving me nuts. It feels like its really buried in the muscle or something. I'm going to try and make an appointment tomorrow. This is making me insane.