Power steering

I seem to have knacked my power steering pump. After changing the fluid it's making a buzzing noise when you put your head near it; sounds like a whine when increasing the engine speed. I'm not as upset as I would
have been if my steering was not now lovely (yet another 'lifetime fill' myth exploded). Strangely enough it was quiet just after the fluid change, only becoming noisy after I gave it a blast around the roads to try it out. I've used Castrol Dexron III ATF.
New one is £256 from Euro Car Parts. Are there cheaper ways to get one or get it repaired? Is there anything I can do for it? I've stripped noisy alternators down before and greased the bearings to make them quiet so I thought about pulling it off next weekend for a look.
It's a 540i 1998. By the way, if anyone else wants to change their PAS fluid, there is a drain plug on the bottom of the pump. This fact which would have made my life easier and possibly saved the pump is NOT mentioned in the Bentley manual. Nor is the fluid capacity, any draining methods, or in fact anything else of value to me, personally, so far.

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