Lotus had developed a system for electric cars to aid in deaf people not getting killed by them.
The recently press released tarted up by Brabus Telsa (the one with the neon lights) had a vroom vroom sound generator in it as well. I still agree with another comment I saw that they need to add a pew pew pew horn to it. lol.
Brabus tunes the Tesla Roadster - yes, you can get neon with that - AutoblogGreen
"Those who get bored with the near silent hum of the electric motor will now be able to get a new "Space Sound Generator" that provides simulated audio tracks including a V8 engine, a race engine or various synthetic futuristic sounds like "Beam" and "Warp." "