The Autohelm/Raymarine wheel pilots are belt driven, even those that have an
enclosed wheel drive.

The ST4000 is of this type and you must realize that the enclosed belt is
going around the inside rim and a few idler pulleys/pinch rollers.

I have had this type of drive on a previous boat and noted similar sounds
and a slight drag. Not enough to effect steering. However, eventually I did
find that the belt would sometimes not release when the clutch lever was
released. To over come this problem, it would frequently require jerking the
wheel back and forth. Later, I found others with this sticking problem and a
solution which involved flushing the wheel drive with a shot of fresh water.
Seems the rubber belt gets 'tacky' over time in the salt air enviournment.


--
My experience and opinion, FWIW
--
Steve
s/v Good Intentions