As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TWO OCCASIONS INFLIGHT, A BURNING SMELL (DESCRIBED AS BURNING RUBBER) WAS NOTICED BY SEVERAL CREW MEMBERS NEAR SEATS 27F AND G. DISSIPATED QUICKLY, COULD NOT BE LOCALIZED OR IDENTIFIED. HOT READING LAMPS WERE INITIALLY SUSPECTED. MAINTENANCE INSPECTED AIRCRAFT. UNABLE TO DUPLICATE SMELL.