The door usually still opens and closes when this starts, which is why people put off the call. What you'll notice is a door that runs unevenly - one side rising a beat behind the other, a scraping sound low on the track, or a roller visibly sitting outside the channel when the door's most of the way up. Sometimes it's quieter than that: just a door that looks slightly crooked in the opening when it's down, cocked a half inch off level. Left alone, the door keeps riding on a track it's no longer seated in, which wears the roller flat on one side and eventually cracks the stile it's bolted to. Catching it at the scraping-sound stage is a track reset. Catching it after the roller's ground itself flat is a track reset plus new rollers and hardware.