2000 lumina engine noise

Hello, When I start the engine it makes a clicking noise (like a knocking) for about 2 seconds and stops then the engine sounds fine. I know its not the oil pressure or valves. Can anyone help? Thanks

3.1's all sound like a can of rocks when you start them cold.

Wait 'till it gets cold out.

They have noisy roller lifters and many have piston skirt slap when cold. Niether hurts anything. Mine's been making racket for 135,000 miles every morning...

Does your car make that noise when its hot too? Mine does it rather if its cold or hot. Thanks