Not enough clearance to the bolts or structures

Reposition the generator with the proper clearance.

Worn or dirty bearings

Replace the bearings.

Worn diode stator

Replace the stator.

Loose generator mounting bolts

Tighten the bolts. If the noise continues, repair the generator.

Loose drive pulley

Tighten the drive pulley.

Misaligned pulleys

Align the pulleys.

Worn or defective brackets

Replace the brackets.