dont know if this is helpful but i had a noise sounded almost like a bad exaust leak at start up , upon further inspection i found one of the hoses from the air pump had a 1 inch slit in it, the noise was bad at start and sounded almost like a bearing squeal after warming up , a 3/4 heater hose 90 deg angle fixed it temporarly till i could get the hose from mb , hope it helps

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1985 190 2.3
1993 300e 2.8