How long does the beeping last? Could it be the reminder that the courtesy lights are on? (Fog lights that turn on after u open and close the door and go away in about half a minute)? Just wondering if it could just be a warning telling u that your fog lights are on without the car turned on, but that's just a courtesy feature and should the beeping should go away once the lights turn off.

Could be way off, but just an idea.