If you find this error:
Whitespace SOAP-ERROR: Parsing WSDL: Couldn't load from yourdomain.com/index.php/api/soap/index/?wsdl=1 Start tag expected, '<' not found .
There is a chance there is a whitespace at the start of your WSDL in Magento inbetween the XML opening tag and the definitions block. The white space is making the WSDL an invalid XML document and causing an the below error.
Aimed at developers : a potential solution can be found here