I agree with Urban Panzer, i have the same noise coming from my 2001 TD5, its been doing it for a year now, a wurring noise, particularly noticeable on left hand turns at low speeds. I can also hear a drone at idle revs but this can only be heard when sitting in car. When running engine briefly with auxiliary belt removed noise is gone. I replaced ACE pump with new and it made no difference so next i put old pump back but deliberately didnt prime it with fluid on re-assembly. I drove the car and it was fine and quiet, power steering perfect then the noise returned after approx 1 mile....when the old ACE pump had primed itself. Fitted new pump again, replaced valve block filter and lived with it since, ACE working fine. The noise only appeared in mine after replacement of all ACE pipes so i suspect either a pipe touching chassis somewhere or crap got into system during pipe renewal and is affecting valve block. Consider doing a few more checks before you fit PAS pump and cant send it back. Hope this helps.