As always it is difficult to tell from a video; but, the noise might be a timing chain tensioner. Suggest not continuing to drive it and taking it to an experienced Benz tech/shop for diagnosis. The tensioner is not a big job but is important to change if that is the problem. If it is diagnosed as a valve lifter instead, then it is a lot less urgent to repair.

Good news is that it doesn't sound like a bottom end/bearing noise.

Good luck and please complete the post.

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