Thanks for your question on Health Care Magic.
I can understand your concern.
Sternum is attached with ribs by cartilagious joint.
It is not fixed and hard joint.
It is somewhat mobile joint. This mobility is important in
rib cage movements during respiration.
On forceful movements, these cartilagious joints can make noise.
So you are mostly hearing this noise. No need to worry for this because this is normal.
Better to avoid such forceful pressure because it can damage these joints.
Since you recently had
cold and pain on deep breathing, better to get done chest
x ray to rule out lung pathology.
If chest x ray is normal than no need to worry for this noise.
Hope I have solved your query. Wish you good health. Thanks.