I have read a lot of sad stories about differentials on those forum. It seems that once it goes bad, it keeps going bad reapeatedly. This is the first time for me. I just got my '04 CTS a few months ago. It was making a whining noise after the car was good and warmed up and driving 20-25 mph it sounded the loudest. Luckily I am still under warranty and I had it fixed yesterday. The service manager told me it was an entirely new unit. And when you look under the car, the center section does, indeed look brand new. Does anyone know if this 'new' unit is really new? Or a rebuild of someone else's bad differential? I'm contemplating trading the car in for a new one, or at least getting an extended waranty because if this is going to be a recurring problem, I don't want to deal with it.