I know this is an old thread, but I wanted to share my solution for this same problem that I've been having since upgrading to the new gingerbread. Note though that this is no longer an issue if you're using the latest google navigation app, but if you're like me and you like to use an offline nav app like CoPilot, then this solution should work for you.
Since this problem was introduced in gingerbread 2.3.3, I thought I would try replacing the libaudiopolicy.so library with one from a gingerbread 2.3.2 rom I had laying around and voila, that seemed to have solved the problem! I haven't tested this thoroughly, but it seems to be working so far. I hope this helps anyone else out there that is still suffering from this issue.