The problem your discribing is an elusive one. Most speculate that it is caused by overheating or the ribbon cable from the keyboard catching noise from the laptops power supply. Unfortunatly I am unable to find a decisive resolution. Some claim the problem was resolved by adding cooling to the laptop, others point to a new keyboard. Most people that have reported this issue have stated that it persists even after reinstalling the OS so I dont beleive its software related. Good luck.