I've had this on every metal-chassis Mac I've ever owned. The chassis typically floats around 50V AC at 50Hz (in the UK, at least) - making it noticeably vibra

I've had this on every metal-chassis Mac I've ever owned. The chassis typically floats around 50V AC at 50Hz (in the UK, at least) - making it noticeably vibrate and tingle when you touch it, especially with the palm of your hands when typing. It also seems to make RSI worse. The solution, as everyone's pointed out, is to ensure you are correctly grounded.