BMT,
I had a very siimilar problem, where my 91 cruiser would groan at very low speeds. I kinda knew that I had a leak in the PS pump, but I was hoping it would go away.... ??? I finally rebuilt it with the help of several peole in the group, and it has not caused my any problems. Believe me, if I can do it, anyone can do it. I think that the kit was like $27, and I also needed a seal, and gasket. I also ended up replacing the outside belt, since I had it off anyway, and It wasn't that expensive. Not too many trouble spots really. Definitely post if you are going to do it.
After my fix, it hasn't leaked or groaned, and it's been like 5 months.
Thanks.
Sony,