really loud....odd. Anyone have this issue? I go to give my kids a little more air and turn the dial up to 3 or 4 and it goes thump thump thump....wierd

 

Hunt around for the threads on rear AC thumping, it is probably a broken blend door actuator.

 

Tebby this is a fairly common ailment-- always is right on the money -it is a classic symptom of a failed blend door actuator. You 'can' fix this yourself and save some money or get a dealer to fix it ( if they charge over $200-$250 you may want to try another). It wont go away or fix itself. the problem is a broken little plastic gear in attached to the motor that is supposed to move the blend door. the thumping is the gear engaging the door a little then hitting the broken teeth and the door slamming back to previous position in a non-stop loop.

one of many threads that has the fix.
https://www.ford-trucks.com/forums/5...ml#post4102647.

or do a search for blend door actuator

cheers