Turn the fan over - don't pull on the power cable to the fan as this can break and render it useless, especially on pre 2014 units. Take a paint brush and brush any animal hairs and dust towards the fan motor and vacuum away. Use a small screwdriver or small Allen key to dislodge any stubborn fluff. Put the fan assembly back in, replace the screws, turn the burner over, pop a small Allen key through the airflap hole and spin the motor to make sure it turns freely without hitting anything.