i have the same noise on my 15 . ck'd. on line and it's another GM prob.and there was some videos on how to fix it on utube .if you have the plastic peace at the front window it is installed with clips about evey 8'' and they get loose and the wiring underneath will rattle also . the fix is to pull off both a+b pillars loose and the plastic peace will un clip then take strips of duct tape the size of the male clip and put the tape on them then replace the plastic strip .ck. for loose wiring while it is off . nothing like DUCT TAPING A NEW TRUCK ''''lol you would think GM would have alot of it ......akarl2 said:Hello, I recently developed an issue with my truck. When I have my dual zone climate control on auto, I can hear a clicking or popping sound coming from what seems to be the front defroster. Its hard to really locate the sound. The sound will go away when I take it off auto and manually turn on the foot and window defrost heaters. I can only create the sound when going 45+ mph and when I move the heat around and up and down in my garage, I don't hear the sound or other issues with the climate control.