Does the slide out use the Schwintek style slide system? If so it could be as mentioned that the gears are not seating with in the track groove and starting to shave away the track a little at a time. It should not be popping.
As for the RV Tech telling you to hold in the button, he is correct in part. With the Schwintek design you hold the button in after it has fully closed or extended to set the gear count to neutral.
Here is link to some good videos from Forest river that offers some great information to various systems of their RVs, including LCI components.
Videos by Forest River RV