Steering pumps can be very sensitive to oil levels, sometimes ridiculously so, not even allowing for 1CM in oil level drop in the reservoir. That sensitivity is noticed first when the wheels are turned outermost left or right as a grinding whizzing sound. Then, as oil levels drop further, the noticeable ailment moves from "outermost wheel position" to an ailment noticeable at the slightest touch of the steering wheel.
Brief, if you want to find things out, make sure you got perfect oil levels first. A tiny leak can cause a lot of trouble. Besides the steering pump, there really isn't anything in that steering system that could make that type of sound, not while parked/idle. For a guy like me, I would have it fixed by a specialist if it were to leak, and would surely send it to the same guy if it was noisy without having detected a leak first. I would say that a noise-without-leak would be a first for me, but I been driving 50 or so modern-ish Jap cars for decades, and may have missed the state of affairs elsewhere.