I have a 2004 FX4 with a strange noise coming from under the dash.It sounds like a high pitched whistling noise and my ford dealership dude told me they have been getting complaints about this from other owners.He told me the cause was cold air coming in thru the heater when the air is dense and it's been looked at by fords cold weather team.It only does this at -20 deg.c or colder so he may be right.Have any of you had this sound .

 

I too have noticed a noise coming from what seems to be
just under the dash between the windshield and the
tray on top. It sounds like air rushing in. There is also a
cold draft in the passenger side footwell, maybe that's
where the air is rushing to..

 

I wanted to let you guys know i have the exact same noise! I've got a 05 Supercab FX4 and i noticed the whistling when the i turn the air cond on. It irritates me. Do any of you guys have any updates as far as a fix?
-Wolf