Mechanism of Korotkoff sounds, bruit.
The Korotkoff sounds heard with the stethoscope during deflation of the cuff pressure between systolic and diastolic pressures are due to intermittent flow of blood in the occluded artery; that is, flow occurs through the occluded artery during systole when arterial pressure exceeds cuff pressure, but no flow occurs during diastole when cuff pressure exceeds arterial pressure. This intermittent flow is turbulent and results in sounds that can be heard with the stethoscope.
Murmurs heard over the heart due to disease processes affecting valves in the heart are due to turbulent flow of blood through those valves. Specifically, turbulence is due to an increase in blood flow rate through a stenosed or incompetent valve. The murmur is best heard in the direction of blood flow through that valve. For example, the murmur of aortic stenosis is typically best heard in the second right intercostal space close to the sternal edge. Note this auscultatory site (called the aortic area) does not correspond to the surface marking for the aortic valve per se.
Bruit is a sound heard over an artery as a result of turbulent flow in it; the cause for localized turbulence is arterial stenosis. For example, carotid artery stenosis may result in a bruit heard over the carotid artery during systole. A bruit in the carotid artery must be distinguished from a murmur originating from flow through a stenotic aortic valve that is conducted to the carotids.