I don't drive a motorcycle, but I really want to and I would say that I know a good deal about them too.
Oh that's cool, I'm scared of them to be honest. Why are they so loud?
Well I think how loud they are depends on the type of motorcycle: street, off-road, or dual purpose.
Which one would be the quietest? That's the one I want. I do like how fuel efficient they are though!
As far as I know, street bikes need to be a certain level of quiet whereas the others don't.
That makes sense. I suppose people in neighborhoods wouldn't like all the noise. 
Oh definitely, noise levels are a big deal. There are also quite a few different designs, like some are better for long distance and some are better for commuting.