FDC2212: reading capacitance value is change +-2pF

Dear Technical Support Team;

I use FDC2212. LC tank inducttor is 22uH and capacitor is 100pF(C0G). 

When I calculate capacitance value with reading FDC value, the capacitance value change +- pico farad.

For example Firstly 100pF then cut off power all system then plug it, reading value change to 102pF.

I think there is a noise problem. What is your suggestion.

Best Regards.