There is an issue that I experienced prior to recent bulletin with THX audio with Nav. System.
After cold period will get no sound although display shows item playing or will get static and sqealing sounds. In most cases will go away with turn off of engine and restart, must reset computer. Dealer replaced 2 of 4 components in my system prior to bulletin of 12/22/08. A software fix is being devloped but not yet available

I really wanted THX/Nav. I would just stay on my dealer untill they get a fix or replace the unit.