My 1996 k1500 sierra has started to make a loud clicking noise and will not stop. After further investigation, I've foun that the small motor that opens and closes the vent flap keeps running and this is what is making the clicking noise. I've replaced the moter and still the same problem. Anyone have any ideas? in the meantime I've disconnected the motor but now the vent is always in the open position so colsld air is always comimg in through the vent.