As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, THE FLIGHT ATTENDANT REPORTED A BURNING RUBBER SMELL. THE FIRST OFFICER WENT BACK TO CONFIRM AND THE SMELL DISSIPATED ALMOST IMMEDIATELY, AND THE FLIGHT CONTINUED. SOON AFTER THE SMELL RETURNED AND THE FLIGHT DIVERTED TO SDF WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIR CONDITIONING SYSTEM AND PERFORMED HIGH POWER ENGINE RUNS WITH THE PACKS IN THE FULL HOT MANUAL MODE WITH NO DEFECTS NOTED.