99 Chevy Lumina engine making whirring sound?

Hey all, hope all is well!

I have a 1999 Chevy Lumina, 248k miles- it was a taxi its whole life, well maintained, i bought it from the taxi place over a year ago and the maintenance record is clean.

While i am driving, my engine is making a whirring sound, especially at low RPM's, that increases and eventually goes away for the most part as i accelerate. It definetly resembles the sound my car made when power steering fluid was out a while ago- so i will add some power steering fluid and see what that does. Is there anything else it could be?

Thanks in advance for any and all help!

-God bless