Fan noise of Inspiron N5110

Hi there, I´ve got Dell Inspiron N5110 which I purchased 5 months ago. Since I´ve bought it, I can hear some noise all the time, before the fan start running. That´s mean sometimes it´s every minute. It´s like 0,5 second long noise, similar like 10 quick cracks or clicks.. I´m not sure, maybe it´s normal, but my friend, who bought same notebook hasn´t notice any noise.  I can´t notice that noise, when is not silence around. But for example at night when is not any noise around it getting be annoying.  Please, does anyone notice similar noise of the fan on Dell Inspiron N5110? Thanks a lot.