There seems to be a delay between the moment the turret upper part rotates until the base really moves.
This is then causing a collision between upper and lower turret, when they are touching each other in a not flush angle.
They do shift slightly in position to each other then and causing stuttering when the base of the turret moves (without itself colliding anywhere else).
{F165}
{F167}
Youtube video: http://youtu.be/pYKuazz5awE
Blueprint of a turret that suffers from this: {F169}