When I change the position of my HVAC from vents to defrost or floor, there is a chattering noise. I also noticed that the system does not completely seal off, because air leaks out other areas, i.e., when I put the system on defrost air leaks out the floor. Any ideas? It is a 2006 F-150 Supercrew 5.4L Triton.

 

Sounds like a "door" has split where the drive shaft fits and the chattering is it popping over to the next notch. Time for a warranty repair. If not under warranty, it could be expensive!

 

Thanks, uknigel2.
I was afraid it may be something along those lines. Thankfully, it is still under warranty.

South