Thanks Forced. I think you got it. There is a pretty bad leak between the exhaust manifold and the turbo. I tried to tighten the bolts to stop it, but the problem must be the gasket (I used the old one). I didn't think an exhaust leak could sound like this, but I bet that is the problem. I will post when I know conclusively and it is fixed.

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1980 300TD with 1985 300TD Turbo motor and 240D 4 speed.