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Budda Bing!! Talked to a local mechanic whom worked at a GM dealer and GM licensed! He said "exactly" that!! LS engines very common "piston slap"! He said, it could last forever or get rid of it while the truck is still worth something! Thanks for the reply Cameron!!!

I have a 2009 GMC Sierra 5.3 L with 185,000 km on it. Cold start, the engine has a low end "knock" but is gone when engine is at normal temperature. Has always run great with no power loss. Could this be a crank bearing letting me know its tired?? Any advice would be great!!!