For anyone who is expeiriancing audio issues with Sprint Navigation after upgrading to 1.3.1 please see this post on the Palm forums.
Sprint Navigation Audio Issues with 1.3.1 - webOS Software - Palm Support Community
One of the tech support members at Palm is asking for a log file from people with this issue to have someone at Palm look at to try and resolve this issue. It only took about 20 days for someone to notice the thread and finally respond to it.