i had a problem when i did my header. I burned through the new gasket it came with. Eddlebrock has them if you need a new donut gasket. its pretty tough to change them out with the header still on the car. If you have the ability to jack the car up, then you can easily take the header off. The hardest part of the install was getting the stock header out of the car. The new one goes in easier. Also I didnt notice that you could hear some air in the Intake
when throttleing up. That is normal. But it sounds like you are leaking. Id change the donut gasket, and possibly the 4port gasket at the top. You may need to dremel the 4port metal gasket if you cant find one that has as big an opennings as the new header. Definately us a metal one for that. Reusing the donut gasket is a bad idea because when you tighten the header onto the mid-pipe they are designed to form fit to the pipes.