Voiceless sounds arise from varied vocal tract constrictions independent of vocal folds

Evidence

The sounds that we produce using some aspect of the vocal tract are not restricted to voiced and whispered vowels. There are many ways to generate sound along different parts of the vocal tract, including clicks, hisses, rolls, whistles, and much more. Between varying the source of the sound (for example, a constriction at the tongue and upper palate) and the shape of the remaining parts of the vocal tract, an infinite variety of sound can be achieved without the vocal folds. — Eric J. Heller, Why You Hear What You Hear- An…, 1727