Susurrus: noun. : a whispering or rustling sound

For example:

Dread creeps in; the ear instinctively fastens on anything, whether fire-hiss or bird call or susurrus of leaves, that will save it from this unknown emptiness.— The Economist, “People crave silence, yet are unnerved by it,” 17 May 2018

I read this yesterday in Paul Johnson’s Heroes.

Reference

Merriam-Webster.com Dictionary, s.v. “susurrus,” accessed November 4, 2020, https://www.merriam-webster.com/dictionary/susurrus.