My 94 e320 estate whines as well but it does it around 40-45mph when coasting or decel down a hill. It's actually more of a whirring noise like the jetsons if anything, really only does it first time out in the morning, so I forget about it after the first few miles. I feel like it's coming from the transmission..

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97 e300d, 78 300Dt, 95 E300d, 94 E320 estate