Crackles heard in clear lungs?

While the crackles could be caused by fluid they wouldn't have cleared witht he deep breathing. Only coughing the fluid out or removing it via the normal excretion process would have removed it. However, atelectasis which is collapsed or partially collapsed air sacs can cause the crackle sound. You have a small receptor in each alveoli or air sac that when you take in a deep breath triggers the release of a very important type of fluid call surfactant the keeps them open. The crackle sound is the alveoli popping open and after you take in a few deep breaths they stay open in normal healthy people. That is why we have patients do a lot of deep breathing and coughing in the hospital when they are laid up in bed.