I think there's an issue with the current RSS feeds where a question is re-added to the feed when the title or other content is edited. I have a few feeds on tags such as
emacs which started getting significant increase in traffic recently. On viewing some of the items they all had recently been edited.
I saw a reference to this specific bug having been fixed in the RSS overhaul question, however the behavior still seems to be occurring.
Here's an example of one of the older items the popped back into the RSS after a title edit: Emacs question
Feed URL being used: https://stackoverflow.com/feeds/tag/emacs
RSS reader: Google Reader