I have a very similar kind. It used to be really bad in high school and has lessened a little over the years (I'm now 30) The grimacing is very familiar and, at my worst it would cause me to jerk my head to the side, and my eyes rolling back a little... What really used to work for me and still does is when I feel one of those blocks coming on is I stamp my foot on the ground. Or smack my thigh with my hand. Looks a little odd but it snaps me out of it. The BBC released a special about stuttering a few years back and I remember seeing someone with similar ticks? For lack of a better word?