Cadillac Forum - Enthusiast forums for Cadillac Owners - 2004 SRX No Audio on Navigation System

I have a 2004 SRX and a few weeks ago I stopped getting any audio out (no sound from speakers). Not with the Radio, CD, DVD or Nav. They all seem to be working and voice recognition commands seem to also be recognised. The one exception is that I am not able to change the balance, bass, or treble through the touch screen on the nav. I hear ding (not from speakers, must be some electronic beep in the nav system) but I am unable to make adjustments. I brought to a mechanic but they couldn't figure it out. I noticed the light for the onstar was on (haven't had service since 05 ... and couldn't have it currently as it is analogue) so I removed all the panels, etc and disconnected the onstar but it didn't help. I thought maybe the radio was being muted by the onstar. I've disconnected the Audio fuse and had the battery disconnected over night. Seems to me like its the radio or the amp.

Any ideas?