That's Wordpress converting quotes to smart quotes. Here's a link on how you can turn them off in Wordpress:
http://www.lancebledsoe.com/how-to-turn-off-wordpress-smart-quotes/
If you want to leave them as smart quotes on your wordpress blog but convert them back for the RSS feed you'll need to add some code to convert them. Here's a discussion of how that can be done.
http://shiflett.org/blog/2005/oct/convert-smart-quotes-with-php