1988 DeVille and power steering issue

[oldsfan]

My DeVille (130K) has developed a groaning sound in the steering. Here’s the history: We had very cold weather last week, and I noticed the sound when I turned into the drive. I checked the power steering fluid, and it seemed okay. I added a little and the noise stopped — for a few days. After the extreme cold left, I noticed the noise again – now really loud at start up (groaning) and then only when I would steer quickly to the left or right – no noise during general run or driving - just initial start up ( a few seconds) and then quick turning of wheel. I thought maybe it was a fluid issue because of the cold. Fluid was dirty -looking - like dirty mop water. I siphoned it out and added new fluid. The new fluid quickly turned dirty, and the sound did not go away. I’m not driving the car until I know what the issue is. Can you help troubleshoot? The car steers fine, but the noise at start up and quick turn of wheel (groaning) is bad. Thanks