Thank you for your question, and I am glad to hear that you have recently had a CT scan
which would seem to indicate that you have already discussed this question with a physician. I would advise you to continue that dialogue with him or her, as they will be privy to additional information that is difficult to obtain or share over the internet. In most cases, common things are common, meaning that you are most likely suffering from a common ailment that can cause swelling, popping, and pain in the cartilages of your thorax. These cartilages are sometimes known as costal cartilages, which explains the name costochondritis, or inflammation of the costal cartilages. This condition is quite common, can lead to swelling and pain as well as a sensation of popping worse with movement. It is also sometime difficult to pick up radiographically. Unfortunately, it is not the only possible explanation, and some of the other possibilities could be serious, and so you will need to continue working with your doctor
to make sure that you are well and do not have another cause for your symptoms. Please speak with your doctor, and I hope you recover quickly.