The thing is the Vcore is rated at NO CPU LOAD. Now this is not possible to detect the Vcore at no load since windows and whatever else is running. As the CPU is in IDLE, that is when the Vcore is its highest. When the CPU is under FULL LOAD, that is when it will be at its lowest. So the fluxuation is for the most part normal. But good regulators and whatnot will help keep it minimal.
iLLz