I watched a bit about this subject on TV this morning and thought then that a little bit of classical music might do the trick. Then again maybe not. Most vehicles owned by teenagers these days can be heard long before the engine anyway. Windows down, speakers full on and blasting out some type of head-banging music (sorry noise, because it's not music). So they wouldn't need to adjust to any new ruling about electric vehicles.
Maybe some sort of cheeky baker's boy whistle would do the trick. Remember when nearly all working men used to whistle on their way to work...
There's no doubt some noise indication is needed for the benefit of the blind etc.
Without noise it would be very eerie if one was stopped on the motorway after breaking down. Just feeling the wind of all the passing silent cars. Then the very nice AA man would probably say. "It doesn't sound too good to me, I will have to tow you to the nearest hearing aid station". Would they be equipped with a stethoscope to locate the problem area?
Maybe this inbuilt noise will be controlled by an on/off switch. So we could switch off when on motorways. But rattling milk bottles? Come on surely we can do better than that? How about rattling beer cans?