Diagnosis
The trolley carriage or the opener's drive gear is worn out. On a belt drive like the 8355W, this is usually the nylon drive gear inside the motor head.
How to Fix It
You need a replacement gear kit (part #41A2036). Unplug the opener. Remove the cover. You'll see the gear assembly on the motor shaft. Follow a video guide to swap it. The job takes about an hour.
If That Didn't Work
The noise is from the door itself, not the opener. Check the door's metal rollers and hinges. A dry, seized roller will grind. Lubricate all moving parts on the door track with white lithium grease.
Heads Up
Do not run the opener with a stripped drive gear. You will burn out the motor. If the motor runs but the door doesn't move, the gear is definitely stripped.