It's constant for a reason, here's an actual crash that I was involved in:
- car ahead of me at a traffic light drives part way in to the intersection on the green light trying to turn left, doesn't get a break in traffic before the light turns. Instead of proceeding safely out of the intersection after the light turned, they did what you should never do and backed out of the intersection. (intentional reversing). Unfortunately they left the vehicle in reverse and didn't shift back to drive. I was stuck in a bit of a dillema, I could see their reverse lights, and had a feeling I knew what was going to come next, but there was nowhere I could go at this point. Light turned green and the person in front of me took their foot off the brake. At this point their car started to roll backwards due to being in reverse, person wanted however to go forwards, so they floored the accelerator pedal. *CRUNCH*.
Your solution of three short chimes wouldn't have helped because she would have expected them when intentionally reversing out of the intersection (a bad idea, but somewhat beside the point here), but without ongoing indication she forgot what gear she was in and behaved as if she were in drive, not reverse. In a Japanese vehicle with the constant audible reminder this would be far less likely as you have a constant reminder that you are in reverse. Setting the volume level to not be annoying, but be a good reminder is possibly an issue, but I appreciate the feature (though it has yet to save me any trouble)