well, it sounds like either a lifter or rocker arm. is it stock? how many miles? I have one that gets loud when the oil filter gets dirty. the oil never gets real dirty, but if I change the filter 1/2 way trough an oil change interval, It gets quieter. If it has some miles, it wouldn't hurt to add some seafoam, it helps keep the lifters freed up.
My brothers 4.0 we done the same thing it sounds like a lifter but the flywheel flex plate whatever u want to call it was cracked.
They usually get a small crack right where the bolt head is which hides it so u have to take it off to inspect it.
The reason it sounds like a lifter is because usually loud and hard to pin point and it turns at the same rpm's as the engine.