Anil,
Not sure what you are referencing. The DNN News Feeds (RSS) module doesn't create the rss feed, it fetches and translates it using an xsl file. So, if you are talking about the internal feed generated, then you should indicate what DNN module you are talking about, as some modules use their own rss news generator.
If it's a feed you are using with the DNN News Feeds (RSS) module, indicate the URL, but it really wouldn't be something that the module actually does, but maybe the xsl. I know from experience that not all news feed sources will validate, as they don't always conform or worry about being used by 'all' news readers, but just the most popular browsers. Not exactly right logic, but that's what I've seen.