I know this thread hasn't been replied to recently, but this JUST happened to me on Friday. Got my complete wiring harness replaced last week at the dealership in my 2009 Sierra. Picked it up Thursday morning, worked fine to and from work. Friday morning everything was fine. Coming home from work on Friday I go to get in and the auto start didn't work, so i unlocked the doors, started it up, and everything worked fine EXCEPT the sound, including the blinker sounds. Go to start it Saturday morning and NOTHING was working, wouldn't start, wouldn't do anything. I check under the hood, and while it was on, the power cable to the battery was not tightened down. Tightened it, made sure the ground was tight, and now everything is working just fine.
I'm thinking you have a loose nut somewhere....