I have an '06 with the Monsoon sound system (no OnStar). I replaced my factory stereo with a Sony CDX-GT340. The radio plays perfectly fine. The cd player and the aux input both act is if they are playing fine, but there is no sound. I checked all of the settings on the stereo itself and couldn't find anything that would cause this. Does anyone know what I may have done wrong or what I can look for, or if I just have a broken stereo? I used the American International GWH-404 wiring harness, and just used the installation kit without the LCD screen (I'm fine without the DIC).