Not required that I know of.
It sounds like it's a combo micro/vent unit (GE etc) I would check to make sure that the motor is properly rotated.
On the micro/vent units the motor on the top can be rotated to exhaust up into ductwork or forward to come out of the vents (usually at the top front ot the unit). If the motor isn't rotated properly the unit will be louder and motor usually burns out prematurely.

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