Alfa Romeo selepeed 156 - 1999. seems to turn over n start to ignite for a sec then starts to click. NE ideas?

dont think it'd be the alternator since it starts to ignite then just goes clicking. could it be the battery even tho its only 3 months old and i turn off all stereo, lights, a/c, anything in the cigarette lighter. anyone got any ideas of what else it could be?