Stealth mode might be occasionally useful, but personally, I want my car to be just loud enough that I can tell when it's running. I've used cars where I couldn't always tell and it sometimes resulted in stupid mistakes like leaving them running when I didn't mean to, or trying to start a car that was already running. It can also be helpful for people outside of the car to be able to hear when a car is approaching. I've never wanted a car to be louder than necessary for those reasons though and whatever noise it makes it shouldn't be annoying or intrusive.