Just went through this. Changed alternator, tensioner assy, bearing in AC clutch pulley-no help. It was the fan clutch.

Here's the thing. I did the "test", starting the engine and shutting it down to watch if it slows down and stops. Spun it freely by hand, no play, etc. Got tired of messing with it and took it to a local shop. Guy started the engine, increased rpm's a bit until it whined, then stopped the fan blades with a gloved hand (he and I don't recommend that lol) and presto! No noise.