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2008 Toyota Siena engine knocking until hot

My Siena is brand new and the engine knocks when cold and under load. I've had it back to the dealer several times and was told each time that the noise is "Normal." It wasn't until I spoke to a Toyota mechanic "Off the Record" that I received a real answer. I was told that the pistons on this engine do not have skirts, which was Toyota's attempt to increase fuel efficiency. The absense of piston skirts causes excessive piston slap until the engine heats up. I am still trying to verify this information. If anybody can help confirm or deny this information, it would be appreciated.

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