Hello-Took a test drive with a 2002 E-150 5.4 Conversion van. Started out with low air flow from the rear air vents (front air flow is fine,both hot and cold), went about 5 miles down the road and suddenly the air flow to rear went from low to high(I had the dial set to rear high the whole time) I didn't touch anything. Went another mile and then I heard a sort of whinning sound coming from the back,it sounded like it was right behind the driver seat(I thought a motorcycle passed me in the other lane,but not)then the sound stopped and all of a sudden the air flow stopped complety to the rear vents(front is fine). What do you think?Is there a rear air motor.Why would I lose the rear air flow and not the front? Sorry for the length-but would this be a deal breaker? Other than this it ran fine. Would this be costly? Thank You.