I've heard this same problem from quite a few A5 owners. I know there's a thread on there somewhere talking about the problem but I couldn't find it. Maybe someone else can? As for things you can do, I think you've done just about everything I would have thought to do. It sounds like there's a bad resistor or capacitor in there somewhere...... EDIT: I found those threads, they can be found here and here.
9/14/12 at 12:13pm