Already done and the fake vroom sounds dumb. Ostensibly the idea for a noise on the outside is laudable so people don't step out in front of a silent car. But it sounds dumb.
And they have the option to play the vroom noise on the inside for the driver experience, even vary the noise by how fast you're going. But again, it sounds dumb like a kid making car noises.
Before the EV thing got serious, the noise was considered. Somebody suggested the sound the Jetsons’ flying car made. I think that’s the sound they need.