Invalid feed

I’ve used feedvalidator.org to validate my feed, but it isn’t valid. The reason it gives is “Blank line before XML declaration”, and the help they provided for this is here. I’ve done everything: I’ve deactivated all plugins, I’ve changed the theme back to default, I’ve looked at wp-config.php, and the feed files, I’ve checked functions.php, but nothing seems to work.

When I view the source, there are 7 blank lines before my DOCTYPE declaration, and I don’t know why they are there.

Has anyone else experienced this problem? And does anyone have a solution for it?

Thanks!