Here's the deal; my truck sounds like wind is blowing through the engine. No matter what, it always has an extremely loud whooshing noise, which gets louder as the RPM's go up. Once I hit 3500-4000, I can't hear my exhaust, my radio, or anybody talking... It's that loud. I have heard it's a vacuum leak by friends and people and mechanics, but nobody can find any leaks. Anybody know a cause of this?