WordNet sense 1 (the light noise like the noise of silk clothing or leaves blowing in the wind):

rustle, whisper, rustling

WordNet sense 2 (speaking softly without vibration of the vocal cords):

susurration, voicelessness

WordNet sense 3 (making a low continuous indistinct sound):

murmuring, susurrant

WordNet sense 4 ((of sound) relatively low in volume):

soft