Hi. i hear a cracking sound in my chest. left hand side and mild discomfort. what could be the cause? my chest feels a little heavy only at night

Dr evaluation : Cracking sound & discomfort/heaviness could be due to a pneumonia infection in the lungs or a small amount of air under the skin layer (usually that occurs after an injury). A heart issue also possible. You need a thorough Dr history & physical exam (including pulse oximetry to check oxygen level) & possibly a chest X-ray & electrocardiogram to evaluate this.

Chest clicking is often from ribs. The heaviness of the chest requires more information. See a doctor