Very interesting discussion about dischargers but it's hard to see how any value of resistance in a discharger - milliohms or megohms - could have any effect on it's ability to discharge the tiny currents and high voltages involved in static build up.
No-one seems to have picked up on Peter's cardinal point: that the crackling is only obvious when there is a carrier present.
Surely this is counter intuitive - with no carrier, the radio's gain will be at a maximum, and therefore most sensitive to noise. When a carrier is detected the radio's AGC will scale back the gain to keep the signal within the radio's dynamic range, avoiding clipping of the am modulation. This reduces sensitivity to noise and should reduce the volume of the crackling - but the opposite happens.
I'm familiar with this same phenomenon in my own aircraft. Can anyone suggest an explanation for it?