Hamman's sign

Precordial crunching or crackling sound, typically systolic and synchronous with the heartbeat, produced by the heart beating against air-filled mediastinal or pleural tissues. Possible causes are spontaneous pneumomediastinum, left-sided pneumothorax, esophageal rupture/Boerhaave's syndrome, pneumopericardium, bronchoscopy/endoscopy, lung rupture from barotrauma, asthma attacks or COPD exacerbations.