Cording elsewhere
I knew about cording occuring in your armpit and experieneced it where it was visible and felt tight to my wrist some days. I started stretching a lot more and was doing pool workouts and it was gone...
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It sounds like cording. I had it in the exact same spot, under my breasts towards my ribs. My physio massaged it with her 'scenar' tool and it worked wonders.