Eek. That sounds bad. That isn’t a fuel knock. That’s bottom end you can just tell. If it was run low on oil, it could very well be a spun bearing.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k