I'm not aware of any statute, it felt very self-regulatory to me.

> Cars are legally required to do so, aren't they?

As an owner of a Tesla, no, there is no such thing (at least in the US), and please stop spreading misinformation (if you are talking about the US).

And the car is not COMPLETELY silent... the wheels make noise on the road. I've driven a completely electric car for at least a year, never got even closely into a pedestrian "situation", and I live in a highly populated area (NYC and its suburbs).

> Cars are legally required to do so, aren't they?

Not yet in the US, though there are active proposals to change that.

> Otherwise, electric vehicles would be quiet enough to kill people.

A completely silent car, driven properly, wouldn't kill anyone.

it is different to have simulated engine noise inside the car and some exterior noises to alert pedestrians/etc that a car is coming

Cars with internal fake noise generally have an option to disable it. There are plenty of gas cars with small, turbo engines that have this noise, it's not particular to cars that are part or all electric.