Just put on a k&n cold air intake this winter. Went on nice and i'm very pleased with it. Although it has almost a wistleing sound to it. It's an extremely loud sucking noise mostly only noticable at idle. Is this loud sucking noise normal? Or is something wrong?

Also I'm getting pretty poor gas mileage, and ive heard people talking about tuning to get better mileage and hp and such. I also heard that with tuning, with every gain comes a loss somewhere else. Are these things true? Where can i get someone to tune my car?

Thanks!