I have a 2005 SCREWw/ 4.6 and I have a very random and anoying high pitch whistle.It has done it at 50-60-70-80 MPH. High rpm and low rpm.
Tried to clean throttle body w/carb clean. seemed to work for about 30 miles.
when it does it if I move the throttle down it will go away.
Anyone have any ideas.

 

My truck does this as well. Only in the winter when it is cold. After reading other threads about this issue it seems that it could be the alternator.

 

This just started about a week ago. 86000 miles and I live in the Northeast.do you think Alt. pulley or the alt. it self?
Thanks

 

I don't know for sure. I haven't really looked into it too much other than reading about it on this forum.

Here are a couple of other threads dealing with this same issue that you may want to take a look at.

https://www.f150online.com/forums/20...d-weather.html

https://www.f150online.com/forums/en...tain-rpms.html