96 hoe does it.119,00 miles. 15-20 sec. Colder it is longer it takes to go away. I asked GM service manager if i would have the same issue with a new crate motor.His reply was I wouldnt till carbon built back up on the piston and causes piston to tilt to side causing the "slap". Guess I'll live with it for now. I've heard V-8 toyotas have similar issue. Still take a noisy Chevy over a quiet ford.