I think you are talking about the area just ahead of the extractor groove
The "crinkle" you're referring to sounds like the case is trying to seperate there.
Take a paper clip and unfold it into a wire about three inches long. Then put a 1/8" 90 degree bend at the end. Use this "feeler" to rub along inside the case wall in the area where you see the "crinkle." If you feel a notch there, the case is trying to seperate.
What kind of brass is this? You say it's now twice fired. It's possible that you are sizing incorrectly, pushing the shoulder back too far. That will cause cases to seperate sometimes in the area you mention.
In any event, don't use this brass anymore. Toss it out.
What kind of rifle are you using? Is it by chance an NEF (H&R) break action?
And if it's Federal brass, it should have been thrown out on the FIRST firing. [img]/ubbthreads/images/graemlins/tongue.gif[/img] [img]/ubbthreads/images/graemlins/laugh.gif[/img]
Edit: Here's a drawing of a case with a hash mark in an area typical of where cases sometimes separate. Your cases may be separating a little farther back, closer to the extraction groove...