Maybe you installed an ebay turbo noise maker one drunken night and didnt know!
Thats exactly what hapened to me! I got a k&n drop in and I was like " WTF IS THAT?!"SE-? said:no, its the intake i swaer. my friends ser did the same thing even with stock airbox, mine does too... its tight tho haha and when i put a kn filter on it got way louder