A little boy in MN was hit by a car in front of his home by a Prius apparently because the car was running silently along on its battery. While the kid was not seriously hurt, the President of the local National Federation of the Blind said sounds should be added to electric cars to save kids, blind people, etc from such accidents.
So what kinds of sounds should be used?
This is my list to get us started:
Roaring tigers
Quacking ducks
Popcorn popping
(Limit three suggestions each, please.)
The first Prius I ever saw, I was almost run over by for exactly the same reason. I didn’t hear it coming.
I vote for synthesized engine sounds, coordinated with the actual operation of the car. You could have a selector switch to choose the type of engine. (“I think I want to sound like a Ferrari today.”) To really confuse things, you could add Harley sounds.
Are the characteristic sounds of vehicles copyrighted?
Don’t quack, d*mn you.
I vote for the Pac-Man noise.
The “thrumming” sound of a Star Trek warp core
the “Vwmmm-Vwmmm” sound of a Cylon Centurion’s scanner eye
the throaty rumble of a V8
I believe Harley Davidson at least tried to do this. I don’t know if they succeeded or not (I seem to remember they didn’t).
I want one that sounds like the TARDIS.
Does a Prius’s quack echo?
No, and no one knows why.
Not popcorn popping… Popcorn the song! Specifically, the 1972 version by Hot Butter, and just the popcorn part, not the bass or other musical parts.
Anything but loud, thumping bass.
Or maybe “Little Duce Coupe,” “409” …except I drive an '86 Volvo.
Dead man’s curve? I guess there’s no shortage of car tunes.
Little Nash Rambler!
What was that one about ‘not being able to get the seat belts off’?
Taking little white pills and my eyes are open wide…
This is a stupid idea to make all cars noisy. It sucks to be blind, but adding more noise pollution to the roadways and neighborhoods is not a good thing. Let’s not forget the bicycles too. Maybe we can go with a dinosaur theme.
I want a calliope on mine.
Mostly 'cuz I think the word “calliope” is cool.
That’s Little Deuce Coupe, FTR.
I can’t believe nobody else suggesting a farting noise. I like the PacMan wocka-wocka-wocka suggestion though 
No, but that didn’t stop Harley for attempting to sue Honda for ‘stealing’ its ‘trademark’ engine sound when Honda came out with their 45º V-Twin Shadow. They failed - legal precedent has been set.
I’ll go ahead and 3rd the PacMan sound - as long as there is occasional, brief, woo woo blue ghost periods.
A Theremin would be fitting, and hard to miss.
Can’t we just put a playing card in the spokes of the wheel? It worked for my bicycle when I was 8.