Are the headset microphone signals travel unbalanced way and how do they reject noise?
The advantage of perfectly balanced differential sources is the induced voltage from a common mode stray current nearby is cancelled. The long cables used on mic’s utilize this for low hum with shielded twisted balanced pair cables.  

Nothing is perfect so the CMRR can be measured in dB attenuation from a specified interference level to compare the best with the  rest.  But these tests are usually only done by EMC experts.

Yes FET buffered mic’s are unbalanced and prone to some mobile charger noise from the SMPS PWM carrier modulation hum from the AC LINE input in some cases.  This is due to the unbalanced coupling capacitance in the high frequency transformer.    Ferrite CM CHOKE donuts help but may not eliminate the hum in all cases with all charger types. You may find these on all VGA cables, some mic’s, some DC adapters and some USB cables.