You should use an RSS module in relevant position if you want to render a third party feed, or grab one from a different part of the same website in question.
To show a relevant page feed (auto-feed articles on your own site), do this:
Add this to the template RSS parameter settings:-
!important. Then edit index.php in the template, usually found at /root/templates/my_template_name/index.php
Find the following line (approx. line 176):
<div id="s5_rss" onclick="window.open('/<?php echo $s5_rss; ?>')"></div>
and change it to...
<div id="s5_rss" onclick='window.open("<?php echo $s5_rss; ?>")'></div>
The PHP variable comes as a multi char string, so you need double quotes. I just swapped them around, no harm, no foul, but you could also just change to double quotes and escape them.
Hit Ctrl + F5 to refresh a page with a menu setup as category blog type for best results.
See an example on www.toowoombarc.qld.gov.au for a large website example, feed icon at the top right, using the new_vision template on J2.5.x.
Hope this helps someone.