Crackling can be a sign of Pneumonia but it can also be heard with lungs scarring and Congestive heart failure and hence crackles are not specific to Pneumonia . Crackling is the collective sounds from various small air sacs so called "Alveoli" that is caused by air passing through pus, blood or any other fluid or scarred lungs.

Crackles heard in the lungs by a doctor means one or more of the following:
1) pneumonia--which can be from infection or inflammation
2) excess fluid or congestve heart failure
3) fibrosis, scarring, or interstitial pneumonitis of the lungs
4) atelectasis or areas of lung collapse

Frequently, yes.

David Sheff, MD/PhD