Metallic rattle at startup
 

There is a very noisy metallic rattle when I start my NC cold. Goes away after a few seconds and doesn't happen once the car is warmed up and started again. If I crank it over a few times with the accelerator all the way to the floor board, and then start it normally this doesn't happen. I tried switching to a lighter weight oil and also using the factory air filter but nothing seems to work. Don't know if it's not getting oil pumped up to the cylinders or if my timing chain is loose. Anybody have any ideas/ suggestions? Thanks.