Breathing noise at rest is usually associated with something causing an upper respiratory tract respiratory airway obstruction. This could result from infection, guttural pouch problems, mechanical problems of the upper airway (displaced soft palate or laryngeal paralysis), or anything else affecting the upper airway. Recently sedated horses often make snoring sounds.

Breathing accompanied by audible sounds usually indicates some obstruction to air flow in the upper airway (versus the lungs). The exception to this is RAO or Heaves in which whistling sounds can sometimes be heard without a stethoscope. These upper respiratory sounds can be described as rattling, whistling, or wheezing.

A rattling sound suggests that there is something interfering with air flow in the upper airway, usually mucus. Snoring sounds usually indicate obstruction of the nasal passages versus the throat. Wheezing indicates air flow through an abnormally narrow passage.