I have an '81 240D manual that makes a "clunking" sound when I shift from 2nd to 3rd and then to 4th. Seems to come from the rear end. After shifting all is quiet and smooth. Anyone have any idea what this noise might be?

Thanks,

Jim

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'81 240D 4-Speed 328K (Daily Driver)
'01 Cadillac SLS 135k (currently up for sale)