http://www.diymobileaudio.com/forum/...es-gm09sr.html

here's the modual for our cars at less than 25% of what you'll see at bestbuy.

 

that does seem to be a good deal but let me offer you a little insight. i am not sure if this is the same across all brands but i have the metra/axxess gmos-04 unit in my car and while it does provide the chimes, they aren't 100% functional. i turned up the volume on the box all the way up but if you are listening to loud music (like me all the time) you can't even hear the chimes because they don't increase in volume with the music. i hope the other brands aren't like this one but if you plan to listen to your stereo loud, then it might not even be worth installing the chime unit.

 

that modual has its own speaker. its the unit i have, its incedibly loud, i mounted mine in the cheek space to the right of the deck where theirs a bubble, theirs dead space their, and it leads out the bottom wide open, i can hear it with my sound system at 100% the unit you have i believe is the onstar unit, that intergrates it like stock so that it goes through the speakers.