I had cording after my original lumpectomy, and after my mastectomy. That stretch exercise where you walk your arms up the wall is great for it. One day when I did it I felt a pop. I freaked out and told the occupational therapist that I was seeing for my lymphedema about it. She said the popping was great as the cording was breaking up. She also taught me to stretch my arm up and feel the cording...it feels like a piece of string(cord)...and to roll the cord between my fingers and this helps to break it up. It worked really well.
Wishing you all the best.
Paula