Abstract: A heating, ventilation, and air conditioning (HVAC) case and duct for passively reducing noise, vibration and harshness (NVH) during operation of the HVAC system. The duct includes an outer wall defining a inner chamber opening into, for example, a passenger compartment of a motor vehicle. Interior walls define at least first and second air passages. A first air stream flows through the first air passage to the ventilation port. The second air passage intersects the first air passage upstream of the ventilation port at an output aperture. The second air stream may flow into the first air passage through the output aperture including a slotted wall to reduce NVH.