|my 1st guess would be crap beneath the keys (dust, hair, etc).|
the easiest way to test if this is your keyboard hardware or some OS/driver issue would be to plug an external USB keyboard into your laptop and see if the problem persists.
If so, you've got a software problem. More than likely, though, you won't have the problem with the external keyboard. the best way to clean your laptop keyboard is with a can of compressed air.