I'm trying to generate an XML output with Zend_Framework, but this nasty thing keeps popping up:

  XML Parsing Error: XML or text declaration not at start of entity
Location: http://cart/index/kurpirkt
Line Number 2, Column 1:<?xml version="1.0" encoding="utf-8"?>
^

As far as I know there are no white-spaces in any of my include files, and even if there were, I think that the ob_clean() function should have taken care of it. Here is my code:

public function kurpirktAction()
    {
        ob_clean();
        // XML-related routine
        $xml = new DOMDocument('1.0', 'utf-8');
        $xml->appendChild($xml->createElement('foo', 'bar'));
        $output = $xml->saveXML();

        // Both layout and view renderer should be disabled
        Zend_Controller_Action_HelperBroker::getStaticHelper('viewRenderer')->setNoRender(true);
        Zend_Layout::getMvcInstance()->disableLayout();

        // Setting up headers and body
        $this->_response->setHeader('Content-Type', 'text/xml; charset=utf-8')
              ->setBody($output);
    }

Any help or suggestions?