First time poster hear, so hello to all. I have an '04 F-150 with a 5.4. When the temp is bitter cold, say below 20 deg mostly, I'll get a whistle sound. I'd say it's a vacuum leak of some sort as I can affect the sound with the throttle. This only happens while driving and part throttle. The Ford dealer has'nt heard my truck do it but they dont seem to be familiar with the problem either. Possible idle air control? I tried to use the tsb button up top but I did'nt find anything there.