I put on in recently and did everything the instructions said. I oiled it and dropped it in yellow side up. The black rubber on one end is longer than the other and I put that in towards the rear of the car. Anyways, after installing it I revved the engine a bit and there seems to be some kind of noise coming from it.
On its way down after revving, at about 2000 rpm the intake makes a pffft sound. Kind of like back pressure?? or something. Anyone no what that is and if it's normal?

 

the only one that does not do this, is the stock system with the stock filter. Is normal, to hear once in a while.