Could this be detonation? Also called pinking, pinging or pre-ignition.
This is normally caused by poor fuel, or carbon buildup in the combustion chambers. I would have thought that the engine management system would accomodate the poor fuel with some kind of knock sensor. I'm sure the techs know lots more about this than me.
Detonation is bad for your engine, it can burn out valves. I would get someone experienced to check this out.
Clattering when cold is usually the hydraulic tappets, but this would go away or reduce when warm.
Sluggish performance is a subjective thing. Have you compared your car with other 180s?