The Horse (Dec. 19) – “Respiratory sounds you can hear without a stethoscope usually indicate an issue in the upper airway, and endoscopy is a common first step in these cases to be able to evaluate the horse,” says Sarah Gray, a boarded equine surgeon at the University of Illinois Veterinary Teaching Hospital.
https://thehorse.com/1118899/whats-that-sound-respiratory-distress-in-horses/