I have three 2011 duramaxs I'm in close contact with mine my dads and a friends and occasionlly they will all lock the doors if we leave the keys in the ignition and shut the door. Mine has done it to me and so has the other two. park the rig, don't lock the door and walk away you get about 10 steps away and the horn honks and its lock with the keys in the ignition. the thing that's odd is it doesn't do it all the time you might go a month without it happening and then bam horn honks and your locked out. you cant make it do it its very random. anyone else experience this? or know about this?