what kind of noise? grinding?
You can buy a rebuild kit. (Ive got an rb20det pump)
The cheap kit for seals does o-rings and gaskets. It retails for around $35.
Next is the rotor and cam ring kit....its the part inside that does the pumping i guess. This is where the grinding noise i would say comes from. For the rb20 it has 2 of these - 1 in the front half of the pump for the power steering, and the rear for the HICAS. The rb20 one retails for $225 roughly, but yours being rb25, it doesnt run hicas off the pump so it will be cheaper.
Id say cost up a good second hand pump.
OR go to Nissan and ask them how much for the o-ring/gasket kit, the driveshaft for the pump, and the bearing at the front.
See here : http://www.skylinesaustralia.com/forums/at...achmentid=31395
Its for the rb20det, but id say it will be the same...