Love the first line.
OK, sounds almost normal to me. Those things are generally not quiet. Does half seem to be a secondary click/scrape sound as if a bit tight but could be normal. Has anyone been digging around inside it?
What is it like if the max slew rate is reduced?
You have few options: Live with it and wait. Take it apart and check and reseat and check all gears are correctly aligned and meshing right. If taken apart the scraping type noise could be the gears are to "tight" with each other. People tend to jam them into place and get it wrong.
Suppose did friend drop it in to you because they have been poking around and got it wrong?
Guess it is a DC motor not a stepper.