I'm pretty sure one has striaght cut spur gears and another has helical gears. The helical ones will be quiter. I heard the striaght cut gears at carlise. Sounded sick to me.....it was kinda loud.
Not at all. With the windows up, and a radio on(not even really loud) you can only hear it at idle and even then not much. To each their own, but I think it sounds freakin' beautiful. I have the windows down almost everytime I drive my car. I brake for a yellow light just so I can sit and listen to it whine(and then do a nice 0-60 pull also).