Mine whistles, but I think it's caused by my cone filter. It sometimes whistles when I mash the thottle also. I like the sound, I've had people ask what is under the hood when they hear it. I just shrug as if I don't know but it's supposed to do that. One guy swore that it had to be a turbine or rotary motor like airplaines use. I just kept him guessing, it's more fun that way.