‘Lub-dup’ sound is produced due to action of

The 'lub-dup' sound is produced by the action of the heart during the cardiac cycle. These sounds, known as S1 and S2, are primarily generated by the closure of heart valves and the resulting turbulent blood flow [1]. The first sound, 'lub' (S1), occurs at the beginning of ventricular systole when the atrioventricular (mitral and tricuspid) valves snap shut to prevent backflow into the atria. The second sound, 'dup' or 'dub' (S2), occurs at the beginning of ventricular diastole when the semilunar (aortic and pulmonary) valves close as ventricular pressure drops below arterial pressure. While other organs like the lungs and esophagus are located near the heart, they do not produce these specific rhythmic sounds; however, instruments like the esophageal stethoscope can be used to monitor these cardiac sounds more accurately during medical procedures [3].

Sources

1. [1] https://en.wikipedia.org/wiki/Heart_sounds
2. [3] https://www.ncbi.nlm.nih.gov/books/NBK541010/