I am hearing a brief whine from under the hood when the car is parked and idling. It reminds me of the noise a vacuum cleaner makes if you put your hand over the hose and it can’t suck. It lasts less than half a second, just long enough to make one of the power steering hoses jump, and happens about every 10 seconds. The belt is in good condition and tight. The fluid level is good and the fluid is clean and not foamy. I have only had to add fluid once, which was about a year ago when I noticed that the noise was related to the power steering hose. The problem has not gotten worse in that time and there are no other symptoms of power steering problems (except maybe some play in the steering?). It’s an '88 BMW 535is.
If anyone knows what this may be and could lend thier expertise, that would be wonderful. Thank you, Carl