Murray....My 93 2.0l 190E had a diff whine after about 20000 kms on the clock. I lived with it till I sold the car with about 90000 kms on iy. It was just as you described, usually on the overrun, I just learned to live with it. Curiously though, the other 2 cars I now have run smooth and sweet !

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1993 190E 2.0L (Euro.) sold
1991. 500 SEL (Euro.)
1991. 300 CE (Euro.) sold
1993. 500 E (U.S. spec.)