If you want to do a quick troubleshoot, remove the wiper arm and see if the spindle finds home without grinding. If it does, reinstall the arm where it normally should sit on the window, probably "advanced" a little on the spindle from where it was. Wear may have disturbed the correct position of the little "timing" disk inside the motor and gear housing.

You may have to pull the assembly (motor and gear housing) if things inside have gotten loose or worn. It's common for the constant slamming of the hatch to cause the screws that hold the housing cover to loosen or fall out. There is also a screw on the inside that will jamb the mechanism if it loosens/falls out. It's a simple mechanism--things should be pretty obvious once you take it apart.