I've got a dry bearing noise coming from one of the Aux belt pulley's, the noise is only there when the engine is revved and is coming back down to idle speed and when its warm.

I've just changed the Aux belt tensioner which made no difference, After I noticed that it juddered quite a bit when running, which its still doing, Could it be it be the alternator pulley freewheel mechanism. I always thought they made a howling noise when faulty.. not a dry bearing noise..??