If I view source on any page of my website, the first line of code is blank. This is causing issues with my sitemap. This may be a plugin, not a theme issue. I just want to know where to look. What theme files or plugins could potentially enter this annoying whitespace in all of my files?
Unfortunately any of your extensions can generate that empty line. The only way to figure out which one is to disable each one and recheck your site source.