cold start engine knock??
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If it goes away after warm-up, I wouldn't worry too much about it.
Your noise is called "piston slap". The cold pistons are moving slightly when they're at the bottom of the stroke. As the engine heats up, the piston skirts expand just enough to stop slapping.
This is perfectly normal for original LS1 engines.
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Given that it goes away with engine warming up it's most likely piston slap that goes away as the piston itself expands with heat.







