I also have felt vibrations only in my case even my DH notices when I'm in vibrate mode, though not many others notice it. So for a long time I thought it really was just sensory. But it is most prevalent when I'm tired, and as yet DH and mother are the only ones to feel it.

My uncle has held an arm or a leg and says he doesn't feel anything, father, brother, sister, cousins and even the doctors, but hubby and mother both feel it. It's slight but there, just a low vibration, a bodily hum if you will. It feels more like it's humming to them then the stronger vibration I feel internally.