My ML have this odd pitch sound which I can pin point to the alternator. I removed the serpentine belt and checked all the pulleys, the pulley on the alternator has no play and spins quite freely. All other pulleys are fine and have no play.

If the alternator bearing goes bad, what would be the symptoms? I would think the pulley won't spin as freely as it should but I don't know for sure.

Any thoughts?

p.s.: the truck has 100k on it with the original alternator. I have replaced water pump and belt tensioner 40k miles ago.

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98 ML320 (gone but not forgotten)