I believe that noise may be a result of a mixture of things... As it occurs when the idle is dropping to normal you have a few things happening. The ignition timing is being advanced until the point of ignition induced knock, then the knock sensors tell it what is too far and retards it back until it smooth out. The level of things electronically and mechanically adjusted on these engines for the power they have is pretty great, and will have some different characteristics than engines that don't have them.

I don't believe it is a sign of excess slack in any bearings, rods or wrist pins as that would be more constant and reproducible at other times.

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2003 4.6is