susurrus

susurrus \su-SUHR-uhs\, noun:

A whispering or rustling sound; a murmur.

Still, the breeze is soothing, as is the susurrus of the branches.
-- Michael Finkel, "Tree Surfing and Other Lofty Pleasures", The Atlantic, March 1998

And there came, like the dry susurrus of wind before thunder peals and lightning, a great rustle of excitement.
-- Richard Whittington-Egan, "The Edwardian literary afternoon: part one", Contemporary Review, April 2000

He heard the susurrus of curtains luffed by the breeze.
-- Erik Larson, Isaac's Storm

Susurrus comes from the Latin susurrus, "a murmuring, a whispering, a humming."