thats the sound of intakes, the stock unit has a chamber built into it that quiets down that sound, its the sound of your motor sucking in air. some intakes with a metal tube are much louder than my iceman with the plastic tube, that helps quite a bit, Ive heard other avengers/eclipses sound completely different and had that whistle while mine is barely noticable

1998 dodge avenger 4 cyl AT
Mods are:
Not enough