They may advise you to vary your routine to avoid putting this particular area under too much strain. I would have a word with a qualified instructor at your gym who will advise you on the best course of action. It's not usually a serious problem but if the joint becomes inflamed it may restrict your training. When you stretch your chest you effectively release the gasses or snap the ligaments/tendons and this will ease the pain. If the sound is a type of popping this is usually associated with ligaments or tendons 'snapping' or sometimes gasses that build up from the fluid of the sternocostal joints (these are the small cartilage type joints that attach the rib to the sternum). It sounds very much like its excessive strain due to your weight training. It seems to me that you wish to stay active, so maybe give it a try.good luck!

Anyway, yoga is good for overall health and wellbeing. Also if you ask a yoga teacher, they can probably help to guide you through postures which are good for opening the chest, which sounds like what you need. Yoga will also give you a more lean muscle build and use and tone your muscles naturally rather than stressfully pumping up at the gym. Stay away from power yoga or astanga or other forms of 'flow' or 'power' yogas unless you are familiar with yoga and know what you are doing.

If you have never done yoga before, try a gentle beginners classes such as Hatha yoga or Iyengar yoga. Yoga - with it's stretching and chest 'opening' postures might be a suggestion. There is little we can do about it, except to keep a healthy balanced lifestyle as much as possible and keep hydrated when exercising. The sternum is the part of our body's bone structure which is most prone to drying out and deterioration in later years in life.

Chest cracking and pain