The Jetson's sound would be a great start.
Would the pitch changes when the speed changes?
There is a new electric Harley that is being shown - it sounds, to me, more like a lower pitched turbocharger whine. You can hear it during a couple of the videos here
Harley Davidson Livewire electric motorcycle taken out for first spin in NYC | Mail Online
Best to avoid that sound ... Harley aggressively guards it's signature sounds ...