What was found
AIRCRAFT WAS GROUNDED: NOSE GEAR DISAGREE IN CLIMB AT ROUGHLY 28,000 FEET. AUDIBLE ABNORMAL AIRFLOW SOUND STARTED SHORTLY BEFOREHAND. NOSE GEAR RED LIGHT INTERMITTENTLY FOLLOWING FIRST ILLUMINATION. BACKUP NOSE GEARLIGHT (ON OVERHEAD PANEL) WOULD ILLUMINATE GREEN WHEN PRIMARY RED NOSE GEAR DISAGREE LIGHT WOULD ILLUMINATE. WHEN TESTING LANDING GEAR LIGHTS IN ACCORDANCE WITH QRH, NOSE AND LEFT OVERHEAD BACKUP LIGHTS REFUSED TO ILLUMINATE AT ALL. ONCE GEAR WAS DOWN ALLLIGHTS RETURNED TO NORMAL OPS. COMPLETED CHECKLIST, GEAR DOWN AND GREEN VERIFIED ON BOTH INDICATORS. DECESION MADE TO RETURN TO ORD, EMERGENCY DECLARED AND LANDED NORMALLY - UNDERWEIGHT. MAINTENANCE REPLACED NLG LOCK ACTUATOR IAW AMM 32-33-21.