Does this happen when you publish to HTML and view it there?
If so, sounds like your background image is not the same as your page size. So, one option is to make it exactly the page size. If your page is 800x600 then if your background image is that size it will not tile.
You can also try this tip from my book on JavaScipt and HTML secrets. JavaScript Communication Secrets
If you want to stop that, create an HTML object at the title level so it will be on all pages. You can shrink it down so it does not get in the way of your design. It is only a place holder.
In the Custom HTML box enter this:
