The rollers are the wear item nobody thinks about until the door gets loud. They are the small wheels that ride in the tracks and carry the door up and down, and after a decade or two of cycles they wear flat, crack, or seize. The tell is noise: a door that grinds, rattles, or vibrates on the way up is usually a door with tired rollers.
How you know it is the rollers
A door that got progressively louder over months, not a sudden bang
Vibration you can feel in the wall when the door runs
Visible wear on the rollers: cracked plastic, flat spots, or a wheel that wobbles on its stem
The door shudders or catches at certain points in the travel
Nylon versus steel
Stock doors usually come with steel rollers, which are durable and loud. Upgrading to nylon rollers with ball bearings is one of the cheapest quality-of-life repairs there is; a door that was waking the house at six in the morning turns into one you can barely hear from the next room. On a door over a bedroom it is the difference between livable and annoying.
Why they wear out
Every open and close wears a little, and in a wet climate the metal parts corrode where they sit. A door that runs a few times a day puts tens of thousands of cycles on the same wheels. Once the flat spots form, the vibration they cause accelerates wear on the hinges, tracks, and opener too.
What the job covers
All the rollers usually go together, because a set at the same age wears at the same rate. While the door is apart, the tech checks the hinges, the track alignment, and the cables, which is the right time to catch anything else before it becomes the next service call. The door should run noticeably quieter on the first cycle.
