I tried a few more RSS feed readers this morning and some do not read the feed and some do. The client specifically mentioned it didn't work in Feedburner. Here is a link to the Feedburner validation error page:
It says, "line 1, column 38: XML parsing error: <unknown>:1:38: XML declaration not well-formed". Perhaps it's this line causing it to fail in other readers?
I looked closer at the RSS validation error and there was an AngularJS variable added to the opening XML tag. It looks like an extension installed called 'Calculoid' was adding it in there. I've disabled the extension and Feedburner appears to read the RSS feed now.