I have it. I never got a formal diagnosis. It's not on every shot, it happens more on shots I'm uncomfortable with, and much more when I'm nervous. It's been seen in dick lane, mike davis, and a few others.
Basically the instant I begin my backswing, and proceed to stroke the ball, it goes away.
It's only during rest/warmup strokes.
At times it feels like my muscle is fighting to stay in the position I know it's right, even though the muscle wants to do something else. I'm fighting what feels natural in favor of a motion that will allow me to stroke straighter.