[support] RSS feeds broken in 4.7.3

Hello,

I'm trying to figure out why my RSS feeds are broken:

" This feed does not validate.

*

line 2, column 0: XML parsing error: <unknown>:2:0: xml declaration not at start of external entity [help]

<?xml version="1.0" encoding="utf-8"?>

Source: http://www.mysite.org/rss.xml

1. 2. <?xml version="1.0" encoding="utf-8"?> 3. <rss version="2.0" xml:base="http://www.mysite.org" xmlns:dc="http://purl.org/dc/elements/1.1/"> 4. <channel> ... "

The problem seems to be that line one is empty - the rest of the XML file is fine, but because the <?xml ...> declaration begins at line 2, the RSS is not valid and cannot be aggregated.

I've tried this with all my feeds, and even the atom.module - same problem.

I've disabled all my contributed modules, unpublished all my non- english content, and still get the same error.

Is there anywhere else I can look for why Drupal is injecting a line of whitespace into my RSS feed?

Thanks,

s.