I’ve been trying to locate the random bong noise for a while, and what causes it, as it’s always baffled me.
After lots of time spent in the car with my partner paying more attention to the screen what we’ve concluded is it’s where the map has some form of road or traffic alert on its live data. It appears you don’t need a destination programmed for this bong to happen, and the “issue” isn’t always visible on the main map screen. However, when you do have a destination programmed you can sometimes see from the progress slider on the side some form of traffic alert symbol. The problem with this, is as soon as it’s bonged the alert “sign” disappears from view.
Certain type of traffic live alerts appear to bing a few hundred metres before, yet others like congestion seem to bong exactly where the slider shows.