Louder than usual idle.

My idle on my 2011 MPB 13" i5 is having a louder idle then when I first got it. It sounds like a low rumble. I have compared it to simllar MBP and it is twice or maybe three times as loud. There is no cd in the drive. The fans are running around 2000 rpm. Only thing I have upgraded is to an 8gb ram. Could it be possible that it is louder because some dust has gotten into the fan? Should I be worried about this louder than usual idle?