Noisy pump are usually due to worn impellers or aerated fluid. Check the fluid for colour and clarity. Gold or pink is good, milky (water) or grey (metal) is bad.

Noise generally increases with workload so it would get louder as you turn the steering wheel while parking. If it really is the pump, put your fingertips or a block of wood against the pump housing with the engine running and have a helper turn the wheel slowly (to increase working pressures). You'll feel the buzz in your hand if it's really coming from the pump.

If the fluid was clear to start with, changing it is not likely to improve things and may even indicate that the noise is elsewhere.