Diagnosing Steering Niggle

[PsYcHe]

Guys,

As per the post on my PF D3, there's a power steering niggle, Before I go off and pay to get it sorted before selling, thought I'd pass it by you lot.

Problem only manifests itself at engine idle, when moving, it's fine, or when you give it even a little bit of gas at stationary, it's fine.

Does that sound like power steering pump instead of rack or servotronic? Will be trying a fluid flush this weekend, but my current suspect is the PS pump rather than the rack (which is good).