Agni Vaisvanara, is the fire within man by which the food that is eaten is cooked, i.e. digested. Its noise is that which one hears, if one covers one's ears. When he is on the point of departing this life, he does not hear that noise.

In plain words: There is a fire inside each person, called Agni Vaishvanara, that digests the food we eat. It is the humming sound you hear when you cover your ears. When someone is about to die, they no longer hear it.