User blog comment:Omega natsu2/Chapter 365: Fairy in the Jail!, Predictions./@comment-7418318-20131222125646/@comment-7418318-20131222135918

It was in the manga too, but we don't really know exactly what that means. It might be after-effects of the scream that knocked her out, it might be some trap that will make it (even) easier for Sindbad to defeat her if they should ever fight again, or it might could even be that someone or something else is the cause of this ringing and we only got the picture of Sin's Djinn in her memory because she falsely assumes it was due to him.

Or it might be the obvious... if you can call something shown for a single frame and then not mentioned for 50+ chapters obvious.