metalic knock

Ever since ive fitted the C20XE into my nova it has knocked from cold. Its a mettalic knock from the bottom end which clears up after 2-3 minutes. Ive been told these engines are prone to a bit of piston slap but im not sure this is the case.
Ill be changing the sump gaskets soon so i might stick some new shellsin when the sumps off as i think this may be the cause.

Any help greatfully recieved

are you sure its the bottom end ? sounds like it could be tappets to me

trust me its the bottom end. I dont have a rattle from my tappets uless its been freezing weather.
Its a dull metallic noise.

if its the sound mine makes i always thought piston slap