Whirlpool ice maker making knocking noise, but still makes ice
I had the exact same issue.  Web search just turned up retailers and drop shippers trying to sell me a new ice maker.  

DO NOT ATTEMPT THIS KIND OF REPAIR UNLESS YOU ARE COMFORTABLE WITH WIRING ISSUES!!  

There are several YouTube videos showing how to remove and replace the ice maker from the freezer.  

What I discovered was a poor connection at the factory wire nut connecting the thermostat to the heating element.  This prevented the heating element from warming up fast enough to free the cubes before the ejection fingers hit the cubes.  Fingers could not move causing the gears to slip.  I simply removed the crimped wire nut, soldered the connection and replaced the wire nut with a twist on type.  Unit has worked great ever since.