I think the biggest issue with white noise is that bikes don't have cabin isolation. If you're trying to make white noise that people can hear through traffic ~

I think the biggest issue with white noise is that bikes don't have cabin isolation. If you're trying to make white noise that people can hear through traffic ~5m away from you, it's going to be really loud to the rider! Music has that problem too, but it's easier to bear or even enjoy, and you can tune it out more easily than white noise. I certainly agree that ebikes can sneak up on you. Personally though, I would give up riding a bike if I had to use a fairly loud white noise generator. Nature sounds would be good for humans, but they might be disruptive to the fauna. Perhaps there's something that can be done about that though.