What kind of turbo? generally smaller turbos won't be that noticable under boost. The BOV SHOULD have an adjustment screw on top that looks like and allen head with a nut around it. All you have to do is tighten it down to make it louder. The tighter you go the more loud and sharp it will be. If it doesn't have the screw then all you can do is buy a different BOV. The best ones on the market are the Greddy type RS, and the Turbonetics Raptor.