Opening day 2013 flagstaff 831 has two slides one open the other one makes a knocking noise when trying to open. I had to crank it a few times then push button to open it the rest of the way. Why was it knocking when trying to slide it open?
Sounds like the pinion gear is jumping on the track gear.
Looks like that model has the thru frame slide. You should be able to see the gears from under the unit. You may have to remove a piece of the coroplast from the underbelly if it's covered.
Salem 29RKSS Pushing a GMC Sierra 2500HD!
Gotta go campin!