Are you feeling the "shocks" when you rest your palms on the laptop, i.e., the area just under the keyboard and next to the trackpad? If so, I experience the same problem once in a while. It's probably just static electricity. Are you using a third-party power adapter? I find that I get these "shocks" when using my MacAlly adapter, but not with my Apple one. Possible explanation: the Apple one has a third prong at the end of its extension cord, which grounds the charge; the MacAlly, with its standard two-prong end, does not.
Hope this helps.