Odd, could you try swapping out your harddrive with your friends and vice versa since you have the same laptop? That would instantly tell you whether its software or hardware. Meanwhile, if you can hook up another monitor and put up afterburner and task manager, check to see what the harddrive, cpu and ram are doing during these dips.
I tried swapping it out. It worked. I reinstalled the game on the original file so some conflict must have been causing the lag. I ran on battery but it just causes constant lag.