Not so much mysterious as baffling. I drive a Prius so there is a huge amount of sophisticated electonics and measurements. Add in self parking and other sensors and it is really complex.

So why do they only have a single fixed pitch 'beep' when something is wrong? Invariably it is followed by a frantic scan of all the lights and panels to find out what the issue is. A double beep for unfasened seatbelts for example, can't tax them too much.