squealing noise when start engine? What causes that. on 1999 Mercedes-Benz C280

When. we start out mercedes the engine makes a loud squealing noise that may continue when we drive it for a period of time. We have replaced the anternator, belt and idler pump

2 answers
most likely the serpentine belt is slipping because the
belt tensioner is failing
may be and over chargibng or over worked alternator,have the battery tested and charging system checked at a benz shop,also make sure the belt and tensioner were replaced with german quality parts not the cheap aftermarket chinees parts