There’s an advert running on the radio the moment for a Lexus hybrid. Although, if I recall Jeremy Clarkson correctly, said car rarely if ever runs off its batteries. The advert obviously doesn’t let that get in the way of its spiel.
Them: “If you listen very carefully you can just about hear...”
Me mentally interjecting: “The sound of hapless pedestrians and cyclists getting mown down because they never heard you coming.”
I’m pretty certain some high end German sports cars play engine noises through internal speakers to “enhance the driving experience”, or sommat. Perhaps stealth motors ought to broadcast an artificial engine noise - like the odour which inserted into otherwise odourless gas - so that others might hear your couple of tons of steel heading their way?