The early V8's on the first model year of the full-size Toyota Tundra have a similar knocking noise, and it was determined by the factory to be piston slap. It disappears once the engine warms up. I wonder if it's the same for your car.

By the way, Toyota says the piston slap is harmless and is not replacing or fixing engines that are affected.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".