#youtube_inline_div secret line

Every time i write a post and click save i get this line under my post:

#youtube_inline_div { position: absolute; display: none; border: 1px solid #999; background: #ececec; padding: 1px; text-align: center; z-index:99}

I have no idea where it comes from. I need to go to the html editor and remove it. If i do it trough the visual editor it will come back again.

Thanks