Volvo s80 making powersteering grinding noise turning in forward and reverse. Reverse was worse. Also worse the sharper I turn. Happened after driving 3 hours on a cold day. It sit over night and had minor similar noise for first few minutes then noise gone. Seems to have self corrected. What is this?

 

Not sure about the noises, grinding noises are seldom good. I'm pretty precise on volvo fluid changes - trans, PS, Brake fluid every 50k. Recently however I somehow skipped my wifes PS fluid on an MDX by 50,000 thousand. Steering started bucking as I approached full lock and would shudder at slow speeds. Fluid change cleared it up with - so far - no ill effects. it's where I would start.