I have a 1989 F150 with a I6 300. I noticed the otherday it had a whine to it. Replaced the serpentine didn't help. Tryed all the pullys thought it was the smog pump, didn't help. I have been looking around at what it could be online and it sounds like it could be a leaky intake manfold, which makes sence since I just replaced my valve cover gasket and had to use make a gasket for the intake. I don't know if this is even possible to get such a high pitched noise out of a intake but if it is let me know, or if someone knows of another common ford problem other than automatic transmission modulator valves and rusty wheel wells. Help me out guys!

 

Not being a smart *** but I got the same exact truck same motor had a whine to it done everything you said you done still didn't fix it so I already had a leaky pressure hose on my power steering pump so I changed the whole pump and its as quit as can be just a suggestion

 

The ford 300 I6 has a gear-driven camshaft. It is inherently noisy. They all make a whining sound - especially when cold.

 

^ This. Mine is the same. Most of them are a bit whiny.