Humming noise in my camry

I have been driving my car now for a few months
(the car used to be my father in laws). The car runs
great, the only thing that i have had issues with is
that the a/c sometimes blows a little warm. Today
while driving it started making a humming noise
that you can slightly hear from inside the car. It
doesnt get louder or stop when i drive faster, or
turn. Could it be the a/c? I turned my a/c off and its
still making the noise.