This is the first time I learn about the existance of this Durst item...
Anyway, to my understanding there only would be sound in case of sparking. The pure built up of high static as well the ion-emitting should be silent.
What counts is the effect. Thus you should be able to watch an effect on static charged items.
Recently I bough an appliance with such module just to use that module apart, but still have not disassembled it. With appliances that got such module I overheard no sound from that so far.