1 The third sound was described as a loud, crisp tapping sound. 2  The fourth sound, at pressures within 10 mmHg above the diastolic blood pressure, was described as thumping and muting. 3  The fifth Korotkoff sound is silent as the cuff pressure drops below the diastolic blood pressure.orotkoff sounds are the sounds that medical personnel listen for when they are taking blood pressure using a non-invasive procedure.