What does it mean if cracking sounds are heard in the lungs while breathing?

Fine Crackles-(formerly called rales). High-pitched, short, crackling, popping sounds heard during the end of inspiration and not cleared by coughing. The mechanism behind these sounds is that inhaled air collides with previously deflated airways and the airways suddenly pop open, creating a crackling sound as gas pressure between the two compartments equalizes.

Coarse Crackles-a loud, low pitched, bubbling or gurgling sound that starts in early inspiration (breathing in) and may extend into the first part of expiration (breathing out). They sound like the opening of a Velcro fastener. Coarse crackles may decrease somewhat by coughing or suctioning but will reappear. The inhaled air collides with secretions in the trachea and large bronchi. These sounds occur in such conditions as pulmonary edema, pneumonia, pulmonary fibrosis, and terminally ill with a depressed cough reflex.