Its not uncommon for cpu-z to report some voltage fluctuation. That's pretty normal. My core voltage has the same .016v dance. Maybe those are the increments cpu-z uses or reads? Speedstep is why when your system is idle it will show the 2Ghz speed. Finally when only using one core only one core will get hot.
CPU-z don't work with my CPU, it always reports Core VID @ 1.225, the funny thing is that if all settings are set to auto in bios CPU-z will report Core VID up to 1.375 and update in real time but as soon as i set the CPU frequency manually it just stays at 1.225