Is the noise you hear kind of a ratcheting sound? If so it sounds like the torque required to move the mount is exceeding the torque applied by the motor. The stepper motors will do this if the mount is out of balance (which is not your issue) or if the gear mesh is tight in a certain location where the worm interfaces with the wheel (sometimes called the ring gear). In this case your mount needs to be adjusted. There are instructions on the Losmandy website on how to adjust the worm mesh for the mount here:
I suggest that you disconnect the motor coupler prior to adjusting the worm and then after it looks and feels good when rotating the worm by hand, then reconnect the motor. I know others on the forum can give you additional advice on how to do this. You can also search the G11 forum for additional information.
If you are not sure about doing this, or want to have Explore Scientific adjust your mount, then you should call Customer Service at 866-252-3811 or write service@...
Director Electrical Engineering
Explore Scientific, LLC.