Thanks for the great feedback!
I really haven't done many sound effects before, this was really my first big attempt. And if I had more time I'd work on the visuals. I'll see what I can do with the doppler, that's a really great idea - and thanks for adding a link!
So I built the game for controller with the analog stick being direction/acceleration and then wasn't sure what to do with the mouse. What I might do is one click to constantly go, one click to stop.
Thanks again!