I have a small clunk / knock that seems to be loudest at the PS pump. I took the belt off and ran the engine again, the noise seemed to be gone although I only ran the motor about 30 seconds since it was at operating temp and my setup is serpentine (therefore the water pump wasn't turning)

When I do hear the noise it is very random (a rod would be fairly regular) and I can't hear it from inside the car.

With the belt off, I found that there was a visible amount of end play in the PS pump shaft (1/16" to 1/8") and I could make a pronounced knock by pulling outward then pushing inward on the pulley. Is this much end play normal in the PS pump shaft? Is this type of noise a reasonable noise to come from a PS pump? (Did a search on these questions, but couldn't find anything definite on the end play question)

Thanks

 

Don't rule out belt noise. It can cause the sound you describe. I've had people bring me engines with a "bad lifter" that were making a clunking noise, random, about 1/2 crank speed. It was the belt. V-belts are more prone to this. The end play sounds typical for a 20 year old pump. There isn't usually any force to pull it in and out except a bent crank pulley.
If the belt is more than a year or two old, spring for a new one and go from there.