Sounds like you have the same problem that my truck has. It's coming from the engine cooling fan. Mine does not do it until it's warned up. When I shut the engine off and the belt stops turning, the fan spins a few times around until it stops. Thats how I found the noise. You then can spin the fan by hand and the noise is there. I just replaced the belt and all idlers hoping to fix the problem. Turns out it's the stupid vicous fan clutch .

I plan to fix this with an E-fan. Hopes this helps unless you already have fixed it.