How loud are the fans?

I have a new mbp. I noticed it gets quite hot on that strip above the number keys, and also to the left of the keyboard. so i figured i would update the firmware. apparantly it is already up to date. but the thing is, i never notice fans comming on. are they pretty quiet, or should i really be able to tell when they are on? i havent listened super carefully, but i also have never noticed any noise.