Tweeti get the same thing from time to time also man. it is especially bad when i go really hard on stretching movements. what i have been told is that the fibers that are holding the pecs to your sternum are just tight and sore from training. if i get my chest busted up with graston or iastm from my pt, i dont have it happen at all for a long time. well that's a good indicator for me that its time to get it done again haha