I have a 2008 Chevrolet Cobalt. The two air conditioning vents in the middle of the front are not blowing air at the same rate as all the other vents. All four speed settings work fine on the other vents but not on the two in question. Could this be a motor issue, or could something be caught in the vent area preventing the air from going through? I just noticed the problem today but don't recall there being a problem before today.