We have a 2008 Sunset Trail Travel trailer and in the fall, the slide wouldn't go out, so we sprayed the rails of the slide with lithium, and they worked really smooth. Now it stopped going out again, but spraying them, we got the slide out, but when it was coming back in, at about 1 foot away from totally being in, it bangs about 3 times, then slides in. Same thing when it goes out, bangs 3 times, then goes out smooth. Any thoughts on what could cause the bangs. Didn't do it in the fall.