DIAGNOSIS The jackshaft bearing at the end of the torsion bar is dry or failing. The opener turns the torsion bar directly.
FIX Unplug the opener. Locate the bearing where the torsion bar exits the wall bracket. Apply a few drops of light machine oil (like 3-in-1 oil) to the bearing's center. Operate the door manually a few times to work it in. Plug the opener back in and test.
IF THAT DIDN'T WORK The noise may be internal gear noise. The 8500W uses a permanent-magnet DC motor with a gear train. This is not user-serviceable. If oiling the bearing didn't fix it, the motor/gear assembly likely needs replacement.
HEADS UP Do not use grease on the bearing. It attracts dust. Use light oil only.