if the noise is a high pitched squealing noise, the belt is slipping....if the noise is a whine or growling noise, the pump is low on fluid or the pump is bad
If you mean "what" is making noise when you turn the steering wheel? It usaually means you need power steering fluid. If you run too long without power steering fluid it will make your power steering go out. If it is making a shuttering noise when you take sharp turns. Your rear differential may need to be serviced. I would have is burnished.
Unfortunately the power steering unit is on the way out.
power steering pump noise,,,may indicate wear
I just got a new power steering pump and my car is making a screeching sound, even after I changed the belts. What noise does yours make
Check your power steering fluid or your fan belt could be making noise.
After bleeding the power steering the pump may make a noise because there isn't enough power steering fluid in it.
Check the fluid first
It could be that the power steering belt is nearing its end of life. You may want to get it (and other belts) inspected for wear.
Pop the plastic covers off around the steering. you will see a contact that is making the noise, add some grease to the contact. I think it's for power to the horn.
It could be low on power steering fluid. That is a common problem. It makes a sharp whining noise when you turn the steering wheel.
Noise may be heard in a power steering line when the power steering fluid is low. Low power steering fluid may occur due to a leaking power steering pump in most cases. If the pump is not leaking, then the fluid needs to be added.
Steering wheel noises can be caused by low power steering fluid. A loose or worn belt or suspension problems can also cause a steering wheel to make noises when turned.