Well here's my two cents. When I bought my truck the intake whistle was almost non-existent. The intake was completely stock, or so I thought. After looking around on here and TDR I saw that you could remove the silencer ring on the turbo to get more noise. So, I go out and try it. Oh, it's already gone!
So, next step on the forums is to gut the stock intake tube. Did it, got a bunch more whistle. There is a silencer in the straight portion of the intake tube that really takes out a lot of the sound. That is your next move.
I still use the stock airbox but cut a hole in the bottom and ran a tube to the front of the truck under the bumper. I also dropped in an AFE filter. It sounds great now.