The contact owns a 2018 GMC Sierra 1500. The contact stated while driving approximately 35 MPH with the rear window defroster activated, there was a burning rubber odor inside the cabin of the vehicle and there was smoke coming from the rear window area. While inspecting the rear window the contact discovered that the rear window connector cover had melted, and the wire connections were a burning amber color, but no flames were present. After disconnecting the electrical connections, approximately 30 seconds later the rear glass panel on the passenger side suddenly shattered. No injuries were reported. The contacts young daughter was seated in the rear during the failure. The vehicle was taken to the local dealer, but the cause of the failure was not yet determined. The manufacturer was not notified of the failure. The failure mileage was 60,952.