Belt-drive Genie opener makes slapping or rattling noise; belt appears loose or sagging.

Safety first: Disconnect power before adjusting belt tension. Do not overtighten the belt.

Steps:

• Inspect belt: Look along the rail. The belt should be snug with minimal sag at mid-span.
• Locate tensioner: At the trolley end or powerhead end, find the tension adjustment nut/bolt.
• Adjust tension: Tighten the nut in small increments until the belt has about 1/4–1/2 inch of deflection at mid-span when pressed.
• Test operation: Run the opener and listen. Noise should be reduced without belt binding.