2004 f150 5.4 . Drove to a friends house 10 miles away used airconditioner first time this season. Got to his house heard a loud whistle in cab. Sounded like a low batt warning that a smoke detector makes. Went home pulled into driveway and it did it again. No warning or engine lights.

 

I have a noise once in a while only when the truck is in drive setting still but it seems
that no one else is have this noise maybe someone will have the problem and
get it fixed my son has good hearing and he says its coming from the center of the
dash but he is only 12 maybe its the samething

 

Hello,

I think I had something very similar to this on my 2004 supercab fx4..The sound was exactly like you described, a whistle being very high pitched. I could not figure out what it was or determine exactly where it was coming from. I took it to the dealer and they said it was a problem with the alternator and that they had already replaced quite a few for the same thing. They replaced the alternator and I have never heard it again. The only thing different is that I never heard that sound when using the AC. I live in extreme northern MN and I only heard it when it was extremly cold. I'm talking like 0-40 below. I hope this helps.....