Hey, I actually took the time to watch your first vids. Sorry. Should have done that. From your description I thought it was something like a trans pump issue but it doesn’t sound like that at all. If I had to guess it sounds like a boost pressure leak.

It seems well correlated with boost pressure (judging from your tach and speedo). The fact you see less in park may suggest less boost = less noise.

Just a wild guess. It definitely sounds like turbo noise. I’d search for a pressure leak (manifold, Alda, manifold o-ring, intake runner seal, switchover valve etc).

You can verify by hooking up a boost gauge by Teeing off your manifold pressure line at the back of the engine. Drive around and check to see if you are losing boost.

Are you making good power?

Also check your wastegate plumbing and actuator. If possible pull the little access cover off the wastegate valve and take a look in there. I think you are on the right track with the turbo.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles