i have gone through every setting on the unit trying to find why the sound is not processing, i believe that the issue is device related now just as you do.....as for the installation, i own/operate a stereo shop and its done right.....the mute is a thought though, ive tried turning the volume up and down while on nav but ive never tried pressing the mute button....i know ive dealt with head units in the past though that wouldnt unmute unless you pressed the mute button again.....ill try it