I had a similar problem with my '94. I emptied the resevoir to clean up all the gunk at the bottom. I cleaned it out, replaced the fluid, and hooked it back up to the hoses. It never seemed to be the same. I constantly had bubbles building up. After a while it seemed to go away, but in the winter especially, it gave me a lot of noise. Eventually the pump died just last winter, almost three years after the little cleaning incident. I replaced the pump and voila, no problems with anything. No noise, no bubbles, no nothing. I still don't know to this day what I did, or if it was just the pump going out.

So in answer to your question, I have no idea what the heck is going on with your PS system but there's my story .