I have the same issue. It’s WordPress that rewrites that portion of the rss feed. It’s coming from this wordpress file **/wp-includes/feed-rss2.php .
It uses this function in writing the title: get_wp_title_rss() (https://wpseek.com/function/wp_title_rss/ ) which populated the “>> sermons” in our case.
I removed the get_wp_title_rss() from feed-rss2.php and it corrected my feed.