01 4.2L f-150.

Has developed and squeal and gets worse with throttle. I have replaced the belt, tensioner pulley and the idler pulley and the problem protists? It doesn't get worse or go away when I turn on the AC nor when I move the wheel, its a somewhat what high end squeal that comes and gos at idle and when actual driving stays about the same constant sound.

Any one have any idea on what it can be? Ill try to make a video of this tomorrow.

 

Does it still squeal when you remove the belt and fire it up? If not, it's one of the accessories, and a mechanic's stethoscope is the best way to find which one it is. I'd suspect the alternator.