RSS feed broken after site update

After a large full-site update, my RSS feed no longer seems to be working. The site uses WordPress as a subdirectory for comments on certain pages. Everything else on the site seems to be working perfectly.

http://www.snowbynight.com/
http://www.snowbynight.com/Journal/feed/

The error message I’m getting is:

XML Parsing Error: XML or text declaration not at start of entity
Location: http://www.snowbynight.com/Journal/feed/
Line Number 3, Column 1:<?xml version="1.0" encoding="UTF-8"?>
^

I’ve tried searching for solutions, but everything I found was 3+ years old and the solutions are not working for me. Thus far I have tried:

– Turning off plugins to see if they are causing the problem
– Switching to the default theme to see if that’s causing it
– Triple checking my php files for spaces above the <?php … ?> code
– Uploading fresh wp-admin and wp-includes folders from 3.8
– Upgrading from 3.8 to 3.9.1

Nothing’s worked. 🙁 Can anyone offer any suggestions?