They sound best when you get that ghostly wail echoing off the trees.  I've heard that effect coming off my dad's little Yamaha 100MX and it's almost scary when you hear it in real life.  You could just 
swear that some unearthly beast is going to come flying over the horizon at over nine thousand miles per hour and rip holes in the space-time continuum.  Then you actually see the bike coming and it's doing about 25 miles per and it's this little tiny thing with a fat guy on it.  Bit of a mis-match, that thing.
Oh, and this video reminds me, I was driving around today, and when I stopped at a red light, what should happen to pull up next to me but a green Kawasaki 500 Mach I triple!  And then his buddy on a blue one pulls up next to him!  I couldn't believe it, I almost started jumping up and down in the car. 
