As the title says, at idle the truck sounds like its humming.. or whining.
Like a fog horn?

You could almost mistake it for power steering except that it sounds like its coming from the top of the motor, towards the rear.
Sound does not change when turning.
If I press the gas the noise changes, but goes away at higher RPMs (1500+)

Ive had other fords sound similar, was fixed with a Idle Air Control valve.

But I dont see anything like that on this motor that could be replaced.
Nothing on the intake looks famaliar like the older motors.

Ive read lots of posts about the same noise, and the cause was the IAC, but does an 08 have one?

I also read it could be the PCV valve. I went to remove that but it wont budge! I can get the hose off, but the valve is not popping out. No movement at all.

 

It could also be a leaking hose. I would do a visual inspection for anything that looks worn or brittle.

 

Figured it out on Saturday....Checked all the usual things. Then using a piece of heater hose from your ear to different parts of the motor we narrowed it down to the alternator.
Same pitch and frequency as the sound we hear
Popped a new one on, problem solved.

In diagnosing I also noted that when running there was 12.8v at the battery.. it should be higher, like closer to 15v. This also told me the alternator had issues.

After the new alternator, its quite and charging at 14.9v

 

. Thank You for the update.