Often an unstable motor is subject to picking up noise from the adjacent cabling. Once the motor is moving the controller can push it back to position, but it can't look ahead to work out that the motor was going to move as some people think therefore, it is important to make sure that the motor is stable without the controller. Make sure that the analogue cables are well away from noisy cables such as the motor commutation cables the noise from these signals can be induced into signal cables even as far as 25mm away. Always use screened signal cables and connect the screen to clean ground at one end only.