The most common type of rale is known as crackles. Rales can be heard with a stethoscope, and they have a variety of different tones that can help doctors determine the cause of the fluid. This fluid can be caused by many things, such as infection, inflammation, or blockage in the airways. Rales are abnormal lung sounds that are caused by the air passing through fluid in the airways. What do rales sound like 4 min read Reading Time: 3 minutes