The 13" has one fan. It shouldn't make too much noise, especially at low speed.
The CPU or power circuitry in the computer can make noise sometimes. there are programs you can download that use a few % of the CPU all the time to keep it quiet. It's a hack, but it might work for you.
http://www.macupdate.com/info.php/id/21714
I also wrote a python script that might do the same thing. I can't test is because mine doesn't make noise, or the CPU is never idle enough for me to experience it. Macs come with python built in, so all you have to do is save the code as a .py file and run it in terminal.
https://forums.macrumors.com/threads/800554/
Alternatively, you can just use itunes since it uses a few % of the CPU while playing music, and the music will drown out the whining sound.
The Magsafe could be making noise too. There's not much you can do if it is, except complain to Apple and see if they will replace it. Using the grounded (3-prong) cable is always good, but it probably won't do anything for noise. Mine sits on my desk next to my MBP, but if you move it to the floor you probably won't hear it any more.
Finally, the LCD backlight inverter sometimes makes noise in Windows in bootcamp. I don't know if the fixed that with the latest drivers, but if not there is probably no fix.
I had trouble playing last.fm on my MBP connected to the inverter in my car. I was using the grounded cable, and I guess there was a
ground loop , because the MBP and the stereo were grounded, so there was an annoying buzz. I didn't have the ungrounded plug, so I didn't get a chance to try it with that. It's possible that the inverter just makes so much electrical noise that the magsafe can't filter it out; it does get a lot warmer runing from an inverter.