ML 320 with high frequency noise
 

So far no luck. Very loud and constant high frequency pitch from engine compartment.

Narrowed sound to left front or vehicle , (passenger side). Not fusbox fan.

Removed fan clutch, serpentine belt to check all bearing, which are fine except for water pump which feels and sounds like it has rocks in it when I turn it.

Started vehicle without belt on and high frequency squeal is still there.

I'm reasonably competent when working on cars and I can say I really don't have any idea what is causing the noise.

Any other ideas would be really wecome.