2000 Chevrolet Blazer Zr2 Cold start knocking from engine

Your oil viscosity might be affected by the cold weather, if you're living in the north, otherwise use oil for high-mileage engines. Higher oil pressure at startup could be due to the oil being thicker at lower temperatures. Make sure you haven't overfilled the oil. Try changing the oil to a recommended viscosity for your climate/mileage and see how it affect the noise. - One other consideration too, is an exhaust leak, it goes away once the vehicle has warmed up. You'll have to put your ear to the engine (mech's stethoscope or long screwdriver) might help just where the noise is coming from.

Vortec piston slap. Most of them do it. Has something to do with the material the piston is made from expanding at a different rate when it warms up. I had a full size that made that noise until it warmed up for years. Never used a drop of oil. Still running at near 250K.