The voltage changes you are seeing are most likely not a problem, and actually are normal. Your CPU has two power saving features, Enhanced Intel Speedstop Technology (EIST) and Intel C-State Technology. The default settings for these in many mother boards BIOS are EIST usually enabled, but C-State in my experience is usually disabled, your BIOS may be different. I think EIST is enabled in your BIOS, and is more commonly used.
EIST when enabled senses when there is very low or no load on the CPU, and temporarily lowers it's clock speed. So instead of running at 2.93GHz, it will run at 2.0 GHz (I don't know the actual lower frequency your CPU will drop to, that is an example), and since the CPU needs less power to run at that frequency, the voltage is adjusted down, as you have noticed. Later, which could be a few seconds, the load on the CPU increases, that is detected and the CPU frequency is set back to it's normal value, and of course the voltage increases along with it, which you again notice. That up and down adjustment happens as long as the load or demand on the CPU is low.
You can check if EIST is adjusting the voltage simply by going into your BIOS and disabling it. Then after rebooting, you should see your CPU voltage staying at one value constantly, or very close to it.
If you are using CPU-Z, you should also see the frequency of your CPU changing when the voltage changes. That is called Core Clock on the same tab as Core Voltage. If that is not changing along with the voltage, then something else may be going on.