I need some help figuring this out so I don't end up replacing everything on the belt drive piece by piece. I have a whining noise that gets louder with engine speed and occurs whether the truck is moving or not. It sounds like it is coming from the passenger side of the truck from somewhere on the belt drive. I've replaced an idler pulley from that side of the engine thinking maybe the grease was gone being its a 140,000 mile truck. It almost sounds like a supercharger but I'm not that lucky. I have a 2004 4.6. What do you guys think?

 

You can remove the belt and spin each pulley by hand is the best way to find it. Spinning it by hand may only sound like a light squeak, but should still be noticeable. I would bet tensioner.

 

You were right. Half of the ball bearings were gone and the seal was broken on both sides of the tensioner pulley.