Squeeling from water pump/pulley

I have a 300 tdi Disco and the water pump pulley sheared. I have replaced the pump and have a loud squeal now. I changed the adjuster, no difference so changed the water pump pulley as it was distorted slightly.
I still have the squeal, it dissapears if I spray WD40 on the belt or water pump behind the pulley, but only for a short while.
Any ideas as what else to change??

Are you sure its the water pump squealing and not the belt itself. Might sound stupid but i had my belt on and it started squealing and i changed everything and it still there till i changed the belt.

What brand of water pump have you fitted?

Water pump is britpart and I have now changed belt, NO SQUEAL result! Didn't think it was that as it wasn't squealing before new pump!
Thanks for your help