how do I keep the audio (radio etc) from playing when all I want is the Navigation voice working?
There is a service bulletin on this. If this doesn't correct your problem then get back to me with more precise information on your vehicle.
The service bulletin is Bulletin No.: 10-08-46-001, Date: January 27, 2010. You can get the full version of the service bulletin at ALLDATAdiy.com
Some customers that were accustomed to previous model vehicles with the "hard mute" feature may be dissatisfied with the function of the "soft mute" feature. For those customers, contact the OnStar(R) Customer Service Center by pushing the Blue OnStar(R) Button to speak to a trained Advisor and request a change be made to the vehicle from the "soft mute" setting to that of the hard or complete muting of audio playback during Turn by Turn directions. OnStar(R) will then create a case number. Advise the customer that the vehicle update should be completed Over the Air within 5 business days, after which an OnStar(R) Customer Care advisor will follow-up with the customer to verify the fix. If the customer does not hear back from OnStar(R) within a week, advise them to press the Blue OnStar(R) Button and ask for Customer Care to check status.