That should be it. The system keeps separate volume levels for media/radio, phone, and sat nav. You may have turned the volume down while 'she' was talking thinking you were muting the radio, but muted the instructions. Set up a route and start turning up the volume as soon as you've initiated the navigation. This should allow you to increase the Nav volume. You can also get it to repeat instructions pressing in the right hand knob, and keep upping the volume.