MY CAR IS MAKING A KNOCKING SOUND WHICH SOUNDS LIKE IT'S COMING FROM THE MIDDLE

Air is moving something around and it's banging against the car.Had a Toyota doing same thing, after LOTS of looking found sensor for inside thermometer flopping around behind grill while driving. OR exhaust pipe hitting floor pan. OR foreign object stuck under car.OR,OR,OR. GOOD LUCK.

Its more than likely a solenoid that controls the a/c door/ gate. Try turning ur temp control about 2 degrees up from the coolest setting. i am on my second nissan titan both of which had that same noise. Basically the Armada and Titan use sMe parts and repaired that problem myself. Do some research in google and you will find the repair to be somewhat easy. Nissan dealors will charge about $700 to fix. Anyways, if u can deal woíth the noise, it wont get worse or create more damage. Gd luck