I remember a few posts in tha past, where someone had a sound that was like clatter or even the dreaded "death knock"...turned out to be the timing belt tensioner saying goodbye, which would also explain the possible circumstance of the timing belt skipping a cog...
pretty sure that was SilverBullet75. He's mentioned it several times.
Search his posts, with "tensioner", it was maybe a year ago or less.
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