Power steering pump buzzing
In most cases, the problem may be air trapped in the system. Its presence is determined by detecting foam in the expansion tank. If it is, then you need to replace the hydraulic fluid or just bleed the system.
Power steering pump buzzing due to low fluid level
The power steering pump howls due to fluid mismatch specifications
The power steering pump is noisy: the reason is the low quality of the liquid
Noisy power steering pump: steering rack check required
Howling power steering pump: power steering belt is loose