2012 Air not as quiet as it used to be

I have been owning my Air since July 2012 (i5, 8GB, 256GB) and it's been always totally calm during regular use (e.g. several Safari windows with multiple tabs open + iTunes + Spotify + iPhoto etc.). I would only hear the fan when I exported a video, play Asphalt or similiar. I think that is all pretty normal and the way it should be. However, the past couple of days I notice that even though I was only running Safari the computer has a constant very low but noticeable noise. The fan runs on 2000 rpm, though.
I don't believe I became more sensitive to noise and I live in a big city so it's not that my surrounding is as quiet as it would be in a library.


Honestly, I don't know exactly how the fan works in the Air and obviously I can't open the MacBook and just vacuum the fan haha.

It's bugging me and I wonder how this would develop during the next months, I mean it can only get worse. So has this happen to you too and it's totally normal or do you have any advice for me on how to handle this best?

Thanks in advance.

Ok, thanks guys. I will bring it to the Apple service provider on Monday as I can't do the weekend without it and I hope it doesn't take them too long to find out what's wrong exactly.

So I had them look at my baby and they found no hardware issue. They cleaned the fan (there was some dust, but nothing too major) and the technician explained to me there is some sort of paste on the processor on which the fan blows so it won't heat up. He applied new paste on it since mine was already a litte drier than expected. He thinks that caused the fan speed up a little.
It seems my computer is ok now again. I will keep an eye on it though.

Thanks for the explanation!