That was my complaint about my Norge's muffler: it was too quiet.
However, I now have over 1,100 miles on my Norge, and the muffler is now noticeable and nicely louder. I do not know why, but it is.
Nevertheless, never content to simply let things be, I ordered an Agostini silencer from Italy. With the decibel killer in, it is quieter than my stock muffler. With the decibel killer out, it is a bit louder (but not obnoxiously so) than my stock muffler. (I say "my stock muffler" because, again, my muffler is now louder than it was when new.)
If you do not yet have many miles on your Norge, you might want to wait. If you do and you are not satisfied, then consider a Mistral or Agostini silencer, but only if you plan to ride it with the decibel killer removed. Otherwise, why bother?
Also, note that the Agostini silencer is MUCH smaller and lighter than the stock muffler, and it is oval-shaped, not round. These two features may be important to you. The Agostini silencer looks a bit odd on the Norge; the proportions are not quite right. Also, because it is oval, if you use your panniers, you will need to use the extension plate that lowers the silencer so it does to hit the left pannier. This in itself isn't bad, but because the Agostini is oval, and because it was designed to install without the extension plate, it will look like an italic O with the extension plate; it will be tilted sideways, and there is nothing you can do to straighten it. (I understand the Mistral is round, not oval, so this would be a better choice if that bothers you, as it does me...)
