Hi all, why is my HVAC fan motor making a humming sound?

I used to hear the same low hum, especially when the AC started up, didn’t think much of it until the sound got louder and the air stopped circulating well. A tech explained that aging motors can develop internal resistance or bearing issues, during our visit, he showed me this link https://tamcoair.com/service/fan-motor-services/ to explain how fan motors behave under stress.