Start by cleaning those 3 little contacts. The signal from the dial passes through those contact to the control board were it's compared to the internal compass signal and drives the motor left or right until they match up.

If you aren't getting a good desired course signal to the board the motor keeps driving looking for a match. When it reaches it's port or starboard limits is when you hear the clicking noise. It's built to slip before it overdrive something and breaks.

Mike