On a number of brush metal laptops/appliances if you run your finger lightly across the surface it creates a vibration sensation in your fingertip; this is not friction it is an actual vibration, I can categorically say that it is caused by some kind of electrical interaction is that the sensation only happens when your appliance is plugged into the AC power which suggest it is something to do with the frequency of AC power, but my question relates to the actual interaction between the metal surface and my finger, what is causing the feeling?