I have a different tac
The grinding noise could be the gear and rack mechanism slipping like it is supposed to when at "end of travel" to avoid burning up the motor.
If the slides have been closed for a long time the seals could be stuck to the walls. The motor torque is just turning the gears and not moving the slide.
Try getting a plastic cake spatula and "carefully" run it arund the slide to try and break the seal loose without tearing it.
Then try the motor again.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW