fordcat

First post. Too bad is has to be ask for help with a problem. Our '07 SEL V6 has a weird problem with the HVAC where we hear a chirping/squeaking from the unit while travelling at speeds above 50MPH. Having the unit in auto or manual makes no difference nor does using AC or not. Fan speed makes no difference either. Turning the unit to "off" kills the sound as does slowing to City driving speeds. Our dealer replaced the fan motor with no results. They are now stumped. Anybody got any ideas?