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I have approximately 10K on the car and I am noticing an engine noise that has me baffled. Baffled because I can't diagnose it and it changes in intensity.

Sometimes when I start the car it makes what sounds like a deep knock and I think: main bearing (gulp). As I drive the sound seems to max as you cross about 23-2700rpm with light load; actually, the lighter the load and the cooler the engine, the louder it seems to be. With a heavy load from a hill or from more throttle the sound is all but inaudible. It actually sounds like a lifter a bit out of adjustment. As the car gets hot the noise subsides to hardly noticable.

My inclination is to just beat the piss out of it and if it breaks - - it breaks.

A few have mentioned piston slap but I have never really heard this and was wondering if this is what it could be or if it is something more ominous.

Oh, I have listened with a stethascope and just the usual mechanical noises - - I suppose what is un-nerving is that it never used to make this noise at all and this make me think very bad things like bearing going south on me.

All comments appreciated.
 

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Check for a small crack at the header flange. That might close up with heat or be lost in the motor sounds under throttle?? If it subsides with heat it must ba a small crack somewhere:huh:

Just a guess.
 

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This was my first thought and I changed the gaskets back to steel and I examined the head for signs of carbon: none.. I know that a loose bole or a small leak can mimic darn near every major problem.
 

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I have an 05 that has the same issue that a Chev svc mgr said was piston slap, "nature of the beast", in addition there is a pinging at low speed take off particularly when going up inclines.
 

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If it gets hotter and the noise diminishes or goes away -mostly- it's piston slap.

You should notice that it is most pronounced under little or no load but under load it is not present . .
 
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