My 94 chevy pick up is making a clicking noise from the heaterbox under the passanger side dash(blower motor area). Itmakes a clicking (open, close, open, closeFlapping noise). Any ideas? It does it on start up and after the trucks shut off. Pretty loud you can hear it inside and outside the truck. Sure is bugging me. Thanks for any help!

 

its the motor that controls the selector flaps there are two more than likley it is the one that controls were it blovs from on the drivers side of the box down low the other just in case is behind the glove box easy way to tell is to unplug them