As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FELT YAW ON CLIMBOUT AT 5,500 FEET, ALL ENGINE INDICATIONS NORMAL AND NO FLUID LOSS OBSERVED. FLIGHT ENGINEER WAS SENT BACK TO CARGO DECK AFTER LEVEL OFF, OBSERVED BANGING SOUNDS OUTSIDE CARGO DOOR. RETURNED TO ORD, FOUND SECTION OF CARGO NET HANGING OUTSIDE MAIN CARGO DOOR FLAPPING IN THE WIND.