Loud enough to hear it over the normal engine noise. You can hear it in the cabin while driving, and on the outside (like when I hung outside the window).

Maybe the word "hiss" is not what I should be using to describe the sound. A hiss typically relates to a vacuum leak, as in a broken hose. The sound is more of a "whoosh", which is why I'm thinking it's the boost being released into the airbox.

What is the longevity of the stockDV under normal driving conditions? Could this one be shot with only 58K miles on the ticker?