Cause:

• Unusual noises can be caused by friction between movable parts, deformed parts, foreign matters getting inside, and defects in belt tension.
  An unusual noise is also made from the fan and the cover bolts became loosened.

Measures:

• Identify the particular point from where the unusual noise is being made, and where necessary treat the problem by replacing parts, etc.
• When operating at slow speeds, a rattling sound can be heard from the brakes, but this is not unusual.