I was in Heidelberg a few years ago, at a German language school. On the Plöck, or Hauptstraße (?) bicycles would stream by way faster than I was walking. Until I learned to stay to the right, I'd hear a ringing bell, then a bike would almost run me over.
Electric cars could have that type of "horn." Indeed all cars should have some type of variable volume horn. A light touch for acknowledgement or gentle warning, more for a more serious warning. Rheostats have been around for a while-- why isn't a variable volume horn even an option?
As one who is not enthralled by "engine noise", I am also not enthralled by hearing every car come into the (for instance) Costco parking lot at 10 AM and every car horn going "BEEP", or even better, "BEEP BEEP" so each person leaving his car will know his car has locked or unlocked. Heavens!
I get a kick out of listening to cars beep, and then adding my double beep right after, to watch the owners turn around and aim the fob again. When they see I am beeping back, I wave. I am so glad Tesla decided they didn't need to add more to the unwanted noise in our lives, while it really ups my entertainment. (Yeah, low threshold.)
I also appreciate it that most every evening, a blower will be on for a half an hour somewhere near my house. A gas blower, with no smog control, putting out what eleven cars put out in the same time driving down the road.
As to "gentle warnings", what's wrong with just driving along behind the person (what are they doing? walking in a parking lot?) until they see you. That's way more interesting, and quiet.
As to bikes, I love it that they ride for their health, and then drive like they have more than a one percent chance of coming out ahead in any collision.