i agree with dimo i ahve been told by my lhs that digitals always try to self centre and that is what the noise is. it is annoying i agree. if the servo is not digital perhaps [a real stab in the dark] your frame rate is too quick for it and it is not able to read signal quick enough so when you add resistance in the form of your hand it interrupts the signal long enough to make it stop? thats all i can come up with. my 2 cents.