P38 diesel engine squeel

For a while my p38 has been making a squealing noise from the engine when it revs above 2500rpm. I have changed the serpentine belt as it was looking tired to no avail as it is still squealing? Any ideas?

Water pump or PAS pump. If its like the PAS pump on the 300tdi then the woodruff key wears and the pully slips forward. Look for damage to the edges of the belt might just be shiney at the moment. Could also try giving the belt a quick squirt of WD40 on the ridges side. It will only last for a short while but useful to see if it is belt related.

Felix