I have a Retina MacBook Pro 13" early 2015 version. I noticed that when the MacBook is on charge there's a strange feedback when I run my fingers over the surface of the MacBook case to the right and left of the trackpad. As soon as I unplug the MacBook's power cable the strange feedback goes away. The feedback feels like there's a slight buzzing going through my fingers. Is this normal or should I schedule a Genius Bar appointment?