Why did the desert sands sing?

What the book reports: On Arabia Petraea’s “Mountain of the Bell,” sand descending the sloping mountainside, whether set moving naturally or by people, was said to produce a musical note^[1][2]. The book compares this with geologist Hugh Miller’s experience on the island of Eigg: walking on white, dry beach sand, he heard a musical sound at each step, just as sand scattered from his footprints^[3].

What the book proposes as a cause: It offers two possibilities, not a demonstrated answer. Moving grains might strike the air and produce countless tiny vibrations that combine into an audible sound; the author illustrates this idea by comparing each grain with a whistling musket-ball^[4][5]. Alternatively, grains might make tiny sounds by striking one another, much as pieces of quartz do when struck together^[6][7]. In either account, the book’s point is that sounds too faint to hear separately might become audible when many grains move together^[8].