Power Steering noises

[jeep lover]

Well, the longer you keep an old vehicle, the more things go wrong....! My '97 Savana Conversion Van, 5.7L engine, 200K + miles, has been wonderful. We have spent $ keeping it up, but in the long run, spent less than new vehicle of comparable size. Besides, it burns no oil.
During the early spring this year, we started experiencing a noise which sounded like "groaning" coming when you turn left or right. I took it in to our regular service center, and they said it was in the steering column, a bushing that needed lubricating, and that it would probably take $500 or so to tear into it, diagnose it and fix it, because they were not dead sure that is what the problem was. They said the power steering pump was operating perfectly, and was not the contributor. Funny thing was, after start up, and running for 5 minutes, the noise stopped and did not come back until stopping, getting cold, and restarting, then the 5 minute moan and nothing. We were told there was nothing seriously wrong, and we could drive it without fear of breakdown. Finally, two months ago, we had some work done on the car by another service center, and they looked at the problem. Their diagnosis was power steering pump with defective check valves. Since the power steering was working flawlessly, they suggested a fluid treatment with teflon in it, to try to unstick the check valves. Guess what, after about a week, the noise stopped. A month later, it gradually started again, finally getting as bad as before. We decided to bite the bullet and change out the pump. I am fairly handy, and although it took me kuch longer than the book hours, got it done. Incidentally, I replaced the entire unit, including EVO, so that I wouldn't have to go through that again. I followed all instructions about bleeding off air, etc. Upon start up, I turned the wheels hard left, then hard right, several times, check fluid level, checked for air bubbles, etc., everything worked perfectly, and no noise. After several hours of intown driving, we stopped and ate in a resturant, came back out and when started the noise came back. Same thing, after 5 minutes it stops. I'm being pretty nice here, left out all the four letter words. Can someone please tell me what the heck is going on?