When a power steering pump starts to make a whining sound then it's usually due to trapped air in the system or your low on power steering fluid.
I would first check the power steering reservoir to be sure the power steering reservoir is full of power steering fluid and not low.
If it's low top it off but don't overfill it.
If it still whines then you likely have a hose leaking air into the system which might only needed tightened down or replaced.