I have a 2018 Silverado LTZ and last night leaving my sisters house my wife heard a hissing sound from the rear seat area. I stopped and listened, turned off the vehicle. Noise stopped. Restarted and noise resumed. Turned around in a driveway and hissing sound changed to a crackling noise smelled burning. Got back to my sisters driveway and looked around the back seat area to see where it was coming from. Started seeing smoke and turned vehicle off again. Shortly after that the right rear window panel shattered. I've never used this system but looked at my vehicle settings and found that it comes on automatically when vehicle is started. I went to my dealership this morning (Saturday) and they said to bring it back on Monday to get the service manager involved. I called GM this morning at the number above and registered my complaint and have a case number. Like many others that have posted here I have no use for rear window defroster but would like to get my rear window replaced.