If you grip the turbo (cold engine of course) and try to wiggle it can you feel any play? On the 85 cali engine the turbo is mounted to the Oxidation Catalyst , but it should also have some supports to the engine block. If those are missing it could make the turbo vibrate. I'll look at my car later and see where and how the braces are mounted.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine