As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD INFLIGHT T1637/02FEB - RECEIVED UNSAFE NOSE GEAR UP INDICATION. COULD HEAR LOUD NOISE WHEN GEAR WAS RETRACTED. SUSPECTED GEAR DOORS WERE OPEN. RETURNED TO ORD AND LANDED WITHOUT INCIDENT. REPLACED NOSE LANDING GEAR STRUT PISTON. SYSTEM GROUND CHECKED NORMAL OPERATION.