Door is very noisy when opening or closing, with grinding or rattling sounds from the opener rail.

Safety first: Disconnect power before working on the rail or drive system.

• Inspect chain/belt tension: Check sag at the midpoint of the rail. Adjust the tension nut so there is only slight sag (per Merlin specs). Do not overtighten.
• Lubricate rail: Apply a light coat of silicone spray or garage door lubricant to the rail where the trolley slides (for chain drive). Do not lubricate a toothed belt.
• Check mounting brackets: Tighten all opener hanging brackets and rail support brackets to prevent vibration.
• Inspect sprockets and idlers: Look for worn or sharp sprocket teeth and replace if necessary.