Mild shock with MacBook Air

I continue to get a mild shock sensation using trackpad with my new mac air. I realize it's "not harmful" except that after a while it actually hurts. It's not an allergy to aluminum alloy, I covered the trackpad. Most noticeable on the 4 fingers usually on the pad, but after a while becomes noticeable elsewhere (I know you won't believe this, but my lips for example). Happens when plugged in (all apple equipment) or when running on battery. Suggestions? I'm toying with an idea for grounding my computer casing.

[Re-Titled by Moderator]