06 Durango with odd engine noise
 

I have a 06 Durango w/4.7L and a KN cold air intake. The intake has been on the SUV for about 3 months. The problem is when I take my foot out of the gas it sounds like a vacuum leak or a turbo blowing off pressure. The dealer told me it was excess air being pushed back out of the intake. Tha sounds like BS to me. Any ideas, plwase help it is driving me up the wall