my '98 is starting to do this. i figured it was from hard driving here in philadelphia (184k mi) but, i don't think it's power steering fluid. mine's just been topped off and it's still doing this grinding/vibrating on hard lefts. i'm thinking like ebo on this. i have my local mechanic looking at this later this week. i was just dealing w/prop shaft issues that may have been related to the bevel gear set afterall. also, i had the front wheels off and noticed a much noiser backlash coming from the transmission. (fluid levels are fine.)
i'll post with the bad news later this week or next.