Susurrus
Etymology
Directly from Latin susurrus, "a murmur, whisper, hum," an onomatopoeic word whose repeated "s" imitates the sound itself. The same root gives us "susurration." English borrowed it whole in the nineteenth century, keeping both the meaning and the acoustic texture of the Latin.
noun · /soo-SUR-us/
A soft, low murmuring or whispering sound.
What it names
The specific hushed rustle of wind in leaves, distant voices, or fabric — a sound that is continuous, gentle, and just above silence.
Example
A susurrus of turning pages rose from the reading room as the lecture began.
Related idea
A murmur can be any low, indistinct sound, including of voices; susurrus specifically evokes a soft, sibilant rustling or hushing.