I have noticed that there is a chirping sound that comes from underneath the truck, possibly from the left side of the front half. It is random but usually occurs on the freeway or when I am changing gears. It sounds like something maybe loose, moving back and forth by the force of the air or vibration...

 

Check the serpentine belt, along with the idler pulley. They can make that type of noise when worn.

 

If it has a 4.2 or a 4.6 it is probably the hamster wheel squeeking.....

At least according to some....

I remember the good old days where a 5.4 was a little engine. I used to have a Z-28 with a 427 stuck in it-that was power!