Hello everyone. My mother's 2002 Volvo S60 2.4(non turbo) Automatic, is making a strange noise that sounds a lot like power steering pump with low power steering fluid. I checked the fluid and it seems to be OK. It is not a constant noise and is very hard to replicate. It comes on at around 50mph. When it comes on and I let go of the gas pedal, it seems to go away. Applying gas pedal seems to bring it back. The noise goes away after 2-5min. And then comes back after 20min or so. The noise sounds more like "hooooooooo" if that helps. Could it be the power steering pump?

Thank you in advance!