To be clear, I do think they should make noise, yes please. Totally agreed. When they're moving slowly enough that people can get out of the way (and the tire noise is a little less significant), they should be making an artificial sound.

Also, Space Invaders sounds would be an amazing choice; along the same lines, the Pac-Man "wakka-wakka-wakka" would be awesome, especially if you have a yellow car. Come to think of it, the Fozzie Bear "wokka wokka!" would be hilarious, too.

I just think allowing people to choose a sound that's automatically blasted at loud volume from their car at any given time is something we've already had a lot of experience with, given that stereo systems have been standard on cars for decades now; and we can be certain that people can't be trusted with it--especially when they themselves can't hear it. There are absolutely people who will use that power to broadcast ads, or their own recorded voice shouting obscenities, or a high-pitched screech sound that harms people's hearing.

Or, even worse, they'll change the sound to silence or something super quiet. Maybe to be malicious, but probably more so just because they find it annoying in some niche situation (like in their garage or whatever).

Allowing people to choose from a certain subset of options, or having some sort of onboard algorithm try to detect whether the sound is an appropriate volume (and replacing it with a substitute if needed) might be a good compromise.

Solid choice.