This is so strange. I have a custom RSS feed that I'm using for feedburner. When I do a Feed Validator check, I'm coming up with a ton of spam at the end of the feed after the closing rss tag. All of this spam is coming from stopdesign.com, however, the author has already removed all of this spam from his site.
Take a look at the validated feed link. Sometimes, you won't see the spam at the end. At other times, you will.