Like @Andrew R Stewart said above –

Disassemble everything and clean vigorously.

While cleaning, thoroughly inspect for any damage to components. In particular look for hairline cracks in the head tube and carbon steerer.

Sometimes the smallest things can create the most noise. I would use a magnifying glass under a bright light and take my time.

If no damage is found, reassemble everything, using liberal amounts of grease, taking particular care to torque to prescribed specifications. Also, I would use fresh cartridge bearings.