XML : PHP SOAP Server somehow adds a LF in front of the XML

I have a small SOAP application that usually works correct on every server. Now I installed it on a PHP/5.5.9-1ubuntu4.14 and it adds a Line Feed in front of the result. My corresponding system cannot parse that misformed xml and generates an error:

  The XML or Text declaration must start at line/column 1/1    

I have absolutely now clue why. Can anybody help me or does anybody have any clue?

Til