These radios use a quadrature volume control not an actual potentiometer.

Quadrature is an A and B channel binary signal where the two channels pulse train is offset by 90*. The processor looks to see that channel is leading and decides what direction you are turning the knob. The more you turn the knob, the more pulses it makes. This system is why the knob can be turned past 360* and has no effect when the radio is off.

The actual volume control is done electronically so a bad control "knob" won't crackle but it will be erratic and jump on it's own.