My 81 300CD did this only when started cold. Was a corroded battery clamp on the negative post of the battery and a loose alternator belt. removed clamp, cleaned and reinstalled. Tightened alternator belt. Please list your type and year of Mercedes in your signature. Was necc to look at your public profile to determine what type/year car you owned.

__________________
81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.