Are all the screws tight in place?

A kitchen exhaust fan that rattles when it is in operation is likely to have loose or defective components that will have to be rectified.

After switching off the power supply, check the fasteners holding the cover in place.

If they are correctly secured, unscrew them in order to remove the cover and check for any loose parts.

Repair or replace any components that you find to be faulty and make sure the screws are properly tightened when you replace them.

Is the drive motor in place? 

• Check the drive motor to ensure it is in place and running properly.
• Check fan and exhaust fan motors as they may be worn.
• The exhaust fan motor bearings might be worn out.
  • To determine if the motor bearings are worn out, try wiggling the motor shaft back and forth. The motor shaft should not move at all. If the motor shaft moves even by a slight amount, the motor bearings are worn out.

If the bearings are worn, replace the motor. Do not attempt to lubricate or repair the motor—if the motor is not operating properly, it must be replaced.