This is the code I was given by a guru to use in the CSS of each board/thread page to remove the scroll 'background':

<style type="text/css"> 
.community { background-image: none !important;}
.pageStyleSheetBG div { background-image: none !important; }
</style> 

If you want to also remove the scroll that appears next to the title, you can include:

.title img { display: none; }

It works for me - hope that helps, Moonbeam :)