If your WordPress website has white space in any of the PHP code then it can cause your RSS feeds to not work, this problem can be caused by faulty plugins, themes or the WordPress files in general. Looking through all of the files removing white space is very time consuming and may not solve the problem. The first time i encountered this problem it was due to white space being added via a plugin, i discovered this by disabling the plugins one by one and refreshing the RSS feed page (Ctrl +F5). The second time however this did not fix the problem.
The solution i have found this time is the addition of a PHP script onto your site which will remove the white space for you
The file needs to be uploaded into your root directory, you then need to edit your index.php file to include the script (see the read me file in the download)
The original source of this amazing fix is: