As all the piece come together to install an after market HU, i.e. the install kit from StreetEFX or the Metra, Soundgate onstar unit, without heavy modification, I just was wandering, when the Nav and Onstar are activated where does the chime audio come from. Is the audio fed from the Nav/Onstar into the radio and back out to the speakers or does the Nav/Onstar have remote to activate a chime device? Any clues????