I have a 2002 Cavalier with the 2.2L 4cyl. I got 2 problems that i need help with

1. I noticed that when i have the AC on, the car revvs while idling.

2.Just recently it started making a humming noise that sounds kind of like an airplane. It only does it when the car is moving. I am replacing brake rotors cuz they are worn, i dont know if the brakes are dragging or not.

Any help will be appreciated!