Expansion and Contraction
Chest freezers may make a popping sound when the compressor comes on. If this occurs, it is considered a normal part of the freezer's operation. The sound is caused by the metal parts inside the freezer undergoing expansion and contraction as the unit operates, much like how hot water pipes operate. Popping noises of this kind are nothing to worry about, and the sound should go away as the freezer continues to run.
The plastic liner around the freezer may also cause a popping sound due to expansion as the internal temperature changes.
Popping noises in chest freezers may also be caused by refrigerant, the substance used to cool the freezer, boiling off as it is being circulated through the evaporator coil. This is also a part of normal freezer operation and is a sign of the freezer unit working properly to cool itself.
Popping, crackling noises may also occur in chest freezers with an automatic defrost feature. If the automatic defrost feature is turned on, it is normal for freezers to make a popping, crackling noise as they defrost themselves. The automatic defrost feature is common among newer freezer models.