I have been told that it is the sound made with the exhaust bypass mod? Someone actually sent me a vid of his set-up with my exact mods and it sounded just like mine. Im going to do a boost leak test this weekend anyway. If it comes up ok then I am going to accept this as normal.

 

Spent a few hours leak testing the car over the weekend. I found three minor leaks (nothing that would rob me of power or make that air gushing noise. My thoughts are if there is a leak large enough to make that sort of noise then the stock K16s would be hard pressed to still achieve my 1bar max boost. So for now I am thinking this is just the sound the car makes running one bar of boost with the exhaust bypass mod. Another member sent me a video that he doesn't want made public and it sounds just like mine so I am feeling pretty good after the boost test that everything is ok.