Indeed, electrostatic speakers are sensitive to humidity. Greater levels of humidity require setting a higher bias setting for optimum results. Should the humidity level fall, it will likely now be too high and you’ll hear the crackling. Just dial them back enough to eliminate the sound.
I maintain a small dehumidifier in the listening room and try to keep the level below 55% so that I don’t have to set the bias particularly high.
As for me, I leave them powered up 24/7 unless I’m on vacation or anticipate nasty storms approaching.