I get that also!
However, for me I finally went to the doctor who told me that I have one rib that I might have fractured at some point in my life which never healed properly.
I don't know if it's the same kind of discomfort I get, because my "pain" radiates through to my back. I was told to get "adjustments" done by a chiropractor but have yet to do so. I just cut down on the amount of ab work I do per week, and it seems to have helped a bit.
?????