This is a bendix going south.
When cold, the grease in the bendix hardens, and does not efficiently pull the starter away from the flywheel. The grinding is the starter rubbing the flywheel at a different speed than engine idle.
Do it long enough and your flywheel will start losing teeth.
While it may be efficient to replace the bendix itself, rebuilt quality starters are available for not much money. Since you have a 240D, changing the entire starter assembly is much easier than on a turbo car.

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