earlier today i put in a DC sports 4-2-1 s/s header. When I drove it I heard a distinct "wooshing" sound. The harder I press on the peddle the louder it gets. It sounded like it was coming from the side, which would be from where the down pipe and cat bolted up. I bolted the manifold nuts and bolts down to 23 ft-lbs. The manifold gasket seemed in good shape besides the regular stains so I put it back on. I made sure the connection to my carsound cat was nice and snug. I had a 3 week old donut in there already so I kept that one. Everything is the way it should be as far as I know. So what could this wooshing sound be? Is it an exhaust leak?