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[JohnGD]

Piston slap maybe? Like the new 3.5L V6.

http://www.remanufactured.com/Engine_Noise_Diagnosis_101.htm

"When your engine is cold, the aluminum piston is small in comparison to it's surrounding iron cylinder. Why? Because with heat aluminum expands rougly 5 times as much as iron. Therefore the rather hollow piston slapping noise will be loudest first thing in the morning. After the engine warms up, the aluminum piston expands more than it's iron cylinder, reducing the excessive clearance between the piston and cylinder wall. So, the test is this:
First thing in the morning, start the engine up and run it for 15 seconds while you listen carefully and memorize the sound and it's intensity. Shut it down quickly, pull the spark plugs and put two squirts of motor oil into each cylinder. Reinstall the plugs, fire the engine up again and listen.

If you have piston slap the noise will have been greatly reduced or even eliminated…..for 15 or 20 seconds that is, and then your nightmare noise will come back like a Marine Corps marching band coming toward you in the parade."

Originally Posted by llPANCHOll

Whatever the noise was it hasnt happened again,
It wasnt normal valve noise, it was a clanking slapping racket..