Holden Commodore: Engine rattle

The engine in my 2012 VE SS Series 2 rattles for 15 minutes after a cold start. Holden has twice told me it is normal and it is piston slap from short skirt pistons. The rattle seems to be getting worse. There is also a vibration after changing into top gear, which seems like torque converter lock-up. No one seems interested in it at Holden.