, I am almost certain I hear this noise when I first open the door, sometimes when driving and I believe after shutting down the engine. .
Mine does this sitting in the garage. IT will do it over and over again - exact same sound like once every 15 or 20 minutes. I have never timed it so that is an approximation. Sometimes when I 'm in the garage all day - I will hear it regularly all day long. I thought it was something with the door locking system but the doors are not locked.
I know when you open and shut the doors the windows will move down about a 1/4 inch and then go back up after closed. it is similar to that noise but the windows don't move.
Nithros described what mine does, I don't usually have the key in my pocket and I don't have the automatic unlock feature. of course I am unaware if it does it when I am not in the garage.... Sort of like the sound of a tree falling in the woods with no one around.