I will try to give you some ideas. First under the slide where you see paneling will the panel come out easily? Sometime the "works" is under a trim panel. Then also with the slide open even slightly, hold open the rubber seals and see if their are any wheels or rollers, if so lube with silicone spray with teflon. On my unit the rear slide is not a full wall slide and is moving only on nylon glides, these will wear out, but spray helped a bunch. I also read on another post to wax the outside walls of the slides with Carnuba brand wax. Not sure what helped the most but the spray and carnuba stopped the squeal.
Let me know what you find.