You-tube to the rescue, searched noisy steering pump and got several returns.
Short version is - screen in pump reservoir becomes blocked causing fluid starvation to pump and whining
Solution, remove reservoir and clean (carb cleaner), replace, refill and....... Result

Managed to spray a little ATF around in the process, but otherwise quick and successful repair.
I have a little noise at full lock on both sides, not sure if this is normal or damage from use prior to repair, but it is very slight.