An abnormal chest sound that is characterized by the clicking, rattling, or crackling noises heard on auscultation of (listening to) the lung with a stethoscope during inhalation. The sounds are caused by the 'popping open' of small airways and alveoli collapsed by fluid, exudate, or lack of aeration during expiration. The word 'rales' derives from the French word rale meaning 'rattle'. Rales can be heard in patients with pneumonia, atelectasis, pulmonary fibrosis, acute bronchitis, or bronchiectasis. Pulmonary edema secondary to left-sided congestive heart failure can also cause rales. [ url:http://en.wikipedia.org/wiki/Rales ]