Hello mate,
It's never loud :) In high revs it does sound really sporty, but still not loud. Inside the car you won't notice any difference at all. A few months ago I recorded some sound clips to make a comparison video, but I used two different cameras and unfortunately my editing program only likes the videos from one of them. Therefore I never finished the video.
It does look mighty, though :D
Edit: Here's one of my short sound clips:
http://www.garaget.org/video/eij6jwp1nkx1
It never stays that shiny for long though..!!