General  Engine / Induction / Exhaust  Suspension / Tires / Brakes  Transmission / Drivetrain / Rear End  What's that knocking noise when the engine is cold?   While the fuel injectors have a distinct tapping noise (usually under higher throttle), at a light load and low speed there seems to be "piston slap" on some people's cars. This occurs in some of the Vette LT1s as well. There doesn't seem to be anything in the service manuals. Most dealers seem to acknowledge the problem and say it's normal which it seems to be. For some reason, the pistons shrink enough in the cold weather so as to "slap" around a little. Once the car warms up, the noise should go away.
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