Could be that your vacuum is too low causing a very hard shift. T a vacuum gauge into the line going to the modulator run it up thru the cowl and lay the gauge outside the windshield where it is visible and go for a drive using varying pedal pressure on the accelerator to see what the vacuum levels are and how they related to the noise. I've driven a 116 where the vacuum level was so low it chirped the tires almost everytime it shifted from 1st to 2nd.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13