This is the sound of venous hum, a murmur heard not uncommonly in children. It is usually best heard just above the right clavicle, and radiates into the neck. You will notice that it is a continuous murmur which does not change from systole to diastole, a slight hum in this example which sounds almost like background noise. The intensity of venous hum can be much greater than you hear now, and may be louder in diastole than in systole. A venous hum which is loud enough may confuse the listener with a
patent ductus arteriosis, another continuous murmur. Typically, the murmur of venous hum can be obliterated by brief digital pressure on the ipsilateral internal jugular vein.
You may hear a slight pause in the hum of this example which is an artifact of the looping of the sound file, depending on your computer.