There are so many different types of alerts or notifications (and it's getting more and more) and they should be distinguishable by the sound they make. Most important, I need a very alarming sound when going off-course. If I'm going downhill and miss a turn, I should hear more than a simple beep.
Best would be if Garmin provided a small library of sounds and the end user could configure one of them for a single type of notification (or even turn it off).
This could even be sold as a safety feature, as it would allow us to concentrate on the road rather than being distracted by the beeping.