Is your engine oil toped off? May sound Stupid but it's well worth it to check. While your at it, you might check all of the fluids.

Maybe spray some WD-40 on the pullies to see if it goes away. The WD-40 will only make it go away for a short time, but if it does go away at all, then you'll have a clue where your problem is.

Does it matter if the truck is cold, warm, warmer, or hot?

Good luck,
GOI

87 Toyota 4Runner-RV Head, Custom Grind Cam, Doug Thorley Header, Keith Black Pistions, 2 1/4" Magnaflow cat, Dynomax Exhaust
2003 Toyota Matrix XRS-Injen CAI