Opener operates normally but there is a loud clunk when starting or stopping.

Safety first: Disconnect power before tightening any hardware on the opener.

• Inspect drive sprocket: On chain drive models, check the sprocket on top of the opener head. Tighten the retaining nut if loose.
• Check rail connection: Tighten the bolts connecting the rail to the opener head and header bracket.
• Adjust chain tension: Remove excess slack as described in the chain tension procedure.
• Inspect trolley stop: Ensure the trolley stop bolt or bumper at the end of the rail is present and secure.