What Causes Vibrating Sensation In Heart After Medtronic Heart Valve Replacement?

I have a Medtronic heart valve replacement. I have experiences a almost vibrating feeling that is especially annoying when I am trying to sleep. My heart doctor has performed stress test and circulation test AND SAYS THESE ARE OK. I sometimes feel this is all coming from the stomach area but feels more like ABIB which the heart doctor says they do not recognize?