I have a 2003 GS300 with the Navi/ML sound system. When I put in a destination and begin, where I should be hearing a voice giving me turn by turn directions, all I hear is the sound of the music I'm listening to cut out briefly when I should hear a voice, but the volume just drops and that's it. Any idea why I'm unable to get a voice from the Navi? I have checked the settings, and the volume is set at an appropriate level.