I have an 05 FX4, has around 50,000 miles on it recently it has a high pitched whistle when its cold out that comes in around 2000 rpm it will come and go with a slight movement of the gas pedal which I think ties it to a vacume problem has anyone else had this happen?

 

my '05 does the same thing when it get really cold out, and has done it since new. I think someone on here said it was the altinator.

 

https://www.ford-trucks.com/forums/7...8-f-150-a.html Yea, I had the same problem and it was a thrust bearing for me. Others had it and said the alternator.

 

I also had this problem last week and through my research of the problem, it seems like the posts like this one seem to start popping up about November/December, when it starts getting cold, as did mine. Alot of the problems seemed to be the alternator. Mine was and had it replaced under my extended warranty last week. Most likely your problem if the whistle goes away after the truck runs for a little bit, as the person who posted before me, his problem never went away after the truck warmed up. So i say to you, if you still have warranty, get the alternator checked an replaced. If you dont have warranty, go get a new alternator and replace it. It will more than likely fix your problem. Good luck!