Thread revival.... but just on the off chance that the OP is still on the forum - did you fix this? I have similar sound and with some help form this forum reckon it might be a bad power steering pump. I haven't lost any noticeable power assistance though - but have a dreadful noise with the belt on (which made me crp myself that it's timing chain/guides....). The noise disappears when the engine warms up and with the auxiliary belt removed... I've changed the water pump and tensioner and idler.... so it leaves the alternator which spins freely and quietly, and the power steering pump which seems to have a "knock" sound when spun by hand... it's about £500 though fro a BMW unit... so want to be as sure as I can that it's the culprit before buying a replacement!