Macbook Air fan noise has a humming sound?

I love my Macbook Air and I always use it to it's capabilites from playing games to running programs and I've gotten used to the fan noise, but recently, today actually, the fan now has a humming sound to it (sort of high pitched and like metal on metal sort of thing) it's as though the faster the fan spins the louder the humming becomes accompanying the fan noise. Any suggestions or ideas? I've read that it needs to be oiled but I'm not sure...

Thanks again.

Braeden