Thanks everyone for the good advice. I went to the tech session and the MB guy said the noise came from the pulley on the tensioner-not the belt. Confusing as the previous session guy sprayed belt dressing on the belt and the noise went away. During this session we pulled the plastic cover off the pulley bearing and sprayed with wd40-less noise! (unless we got overspray on the belt.) Will have to do some more work.