DIAGNOSIS This is likely worn gear and sprocket assembly noise, exacerbated by the load of lowering the door. The plastic gear inside the opener is designed to wear out first to protect the motor.
FIX The unit requires a gear and sprocket replacement kit. Model 41A2034 is the common kit for this chassis. You must disconnect the opener from power and manually disengage the door carriage before starting. Follow the kit instructions to replace the plastic drive gear and the associated metal components.
IF THAT DIDN'T WORK If the noise persists after gear replacement, the issue is external. Lubricate the door's metal rollers, hinges, and springs with a silicone-based lubricant. Do not use grease or WD-40. Check for binding in the tracks.
HEADS UP Continuing to run the opener with a stripped gear will damage the motor. The unit will eventually stop moving the door entirely. Replace the gear kit at the first sign of grinding.