Sounds similar to what my large slide would do but I got most of my noise when starting in. What was happening in my case was when the slide was fully extended it would sag just enough that the upper edge of the slide would actually extend under the cutout in the sidewall catching on it. I solved my problem by attaching a flat piece of metal to the back side of the upper slide lip extending it high enough so that it limited on the wall and keeps it from catching.