A vehicle heating, ventilation and air conditioning system includes a plurality of ducts for providing conditioned air to an interior of a vehicle. The plurality of ducts includes a window defrost duct and a floor duct. The system includes a mixing chamber upstream of the window defrost and floor duct. A damper is selectively controllable to distribute the conditioned air to one or more of the plurality of ducts. The damper is configured so that when in a floor only mode position, the damper directs conditioned air in the mixing chamber only to the floor duct. A bypass conduit is configured to direct air from the floor duct to the window defrost duct when the damper is in the floor-only mode position. The conditioned air directed through the bypass conduit attenuates noise generated in the mixing chamber from emanating to the window defrost duct.