As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF LOUD BANGING NOISE HEARD BY CABIN CREW IN FWD SERVICE DOOR AREA. NOISE GOT LOUDER WITH INCREASED AIRSPEED. AIRCRAFT RETURNED TO PDX AND FOUND FWD SERVICE DOOR STRAP OUTSIDE A/C THROUGH HINGE. FOUND SIX INCHES OF SAFETY STRAP PROTRUDING FROM LOWER HINGE. NO DAMAGE NOTED AND SEAL OK. STOWED STRAP.