each dnn module has an expiration date, those are part of the general module settings, not the specific module settings. Since rss works through the search interface, and since search does not index module that have an expire date set, rss will not work properly either.
I did not mean doing anything differently in specific announcements.
To date, i have never found problems with rss with the announcement module, so if rss is not working, it is most probably an issue with the search indexer not running, or ignoring the module alltogether