dell studio xps 1340

Hi, i just got the dell xps 1340,

500gb hard drive,

nvidia 9500 m sli

core 2 duo 2.53 ghz

4gb ram

and so far i have no problems with it. I just had one question i was wondering about. When playing games, the fan gets pretty loud, and shortly after that the laptop starts to make additional noise, as if it was pulsing. You can feel it on the chasis, its as if its like a heart beat or something. (dum, dum, dum, dum) with about a one second pause in between 'dums'. when i have my wrist resting on the chasis near the touchpad i can feel it sort of pulsing...

In nvidia system monitor when i check gpu temp after gaming it is never above 80 celcius...

was just wondering if anyone else has experienced this, and if it is normal. 

thanks again.