All of a sudden. Wasn't there when I left last night but was there when I got to my destination.

It is pretty loud, and it is constant not intermittent. The sound really does remind me of a chain being drawn over metal, and I am fairly certain I heard a few metallic "pings" while the engine was idling. I heard this ping once or twice, but I can not swear by it. This ping was not loud.

I am not at home either right now, so I do not have access to tools... I will keep answering questions and find ways to pass the time.

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1984 300D Turbo.