I'm originally from Melbourne, though have been at the Gold Coast for the last 2 months, and my girlfriend has been driving my VY Exec which had this problem with the horn going off. I've been reading this site for a while and when my girl told me about what happened I guessed it was the same problem as you have described. My girl went into Holden and told them about what we thought it was and when she went to pick up the car, it was exactly that. Apparently the heat caused the sticker to peel back. Thanks guys.