When I had mine, that told me that it needed to be cleaned, but that might not be your case. Try using the three pronged adapter, and if it continues, I wouldn't worry about it unless it really bothers you.
Nah. I've got Carpel Tunnel Syndrome and it's quite distinct because you can feel the pressure about two inches up from where your wrist joins your arm and there's other stuff I won't bore you with.
This sounds actually dodgy and you should take it to a "Genius" bar and get it checked out. Or check the recall for the power adapters.