Markus KellerNot 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.03-28-2008 06:17 PM
Just an added note: I have been caught identifying this type as "internally vented" and the motor or diverter installed incorrectly because the air did not blow out the front of the unit. No visible duct from above, in the wall cabinet. Some of these are able to be ducted out the back of the unit to the exterior. Keep and eye out for the additional vent in the attic or on the exterior wall if you see this condition.