You may want to check other index files too, root index.php, index.template.php of any and all themes, and so on. And if you find the matching code, copy the code here including a few lines before and after.
Also check the folders for any files that you do not recognize, or have been modified very recently.
When did this appear?
Was it immediately when you installed the theme, or later?
Where did you get the theme from?
Does it appear if you switch to the default (curve)?