Stepper motors increase speed when touched.

Hi,
I'm working on a robotic arm and just hooked up my elektronics. All the steppers move just fine, but when I touch the motors they crank up the speed. What could be the cause of this? I've heard of driver IC's being sensetive to static but I can't understand why the motors would react like this when touching the motor casing!

Hope you guys have some explanation for this.