Air Conditioner problems of the 2006 Chevrolet Silverado 2500

The contact owns a 2006 Chevrolet Silverado 2500. While driving 50 mph, the contact heard a loud whistling noise coming from the passenger side vent when the heater was activated. The dealer was unable to diagnose the failure; however, they replaced the vent cover. The failure persisted. He took the vehicle to the dealer and they stated that the taping or molding around the heater core may have caused the failure. The dealer sprayed silicone on the dashboard; however, the failure continued. Approximately eleven months later, the dealer inspected the vehicle and stated that the failure was a normal occurrence. As of November 27, 2007, the dealer had not repaired the vehicle. The failure mileage was 10,000 and current mileage was 13,635.