As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BURNING RUBBER SMELL IN AFT CABIN. SMELL DISSIPATED WITH RECIRCULATION FAN SWITCH IN OFF POSITION. CHECKED AFT LAVS, AFT GALLEYS AND OVERHEAD CEILING COMPARTMENTS AND GALLEYS. RAN BOTH PACKS WITH APU AND ENGINE BLEEDS. COULD NOT DUPLICATE. PLACARDED RECIRCULATION FAN PER MEL 25-31. REMOVED AND REPLACED RECIRCULATION FAN. PLACARD CLEARED.