Sloane Atkinson is awaiting a donor heart. Doctors dismissed a newborn’s “grunting” as normal sounds — but six weeks later, the baby was intubated in the PICU, and is now awaiting a heart transplant.

People usually don't give much thought to sounds at the gym or on a sports court—clanking weights, squeaking shoes, background music. One sound in particular that's common background noise in these ...