Odd steering sound

I've heard an odd sound recently whist steering to the right.

I don't need to be at full lock, the sound can be heard at virtually any amount of steering input but I do need to be on the accelerator. Coasting along there is no sound at all. The sound seems random in nature, but there are certain corners where I will hear the sound more often than others. It can only be heard for 1-2 seconds maximum then it's gone. It also doesnt happen every day and never happens when moving slowly.

It sounds like someone playing a school Recorder flute!

Any ideas? Has anyone encountered this before?

I'm going to replace the PAS fluid to start with as I don't know when it was last changed.

If it's the pump, is there more steering load turning to the right than left?

Most likely to be the pump whining. Try a fluid change and see what happens.
Most roads are cambered to the left. This could cause a slightly higher load on the pump turning right, compared to turning left.