As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED. (SMELL) STRONG ELECTRICAL OR RUBBER BURNING, PRECEDED BY A RUMBLING SOUND FROM BELOW THE FLIGHT DECK. HAPPENED TWICE. DECLARED EMERGENCY DURING APPROACH TO CLT WITH CABIN ODORS. MAINTENANCE FOUND AVIONICS FAN FAULTY; WHICH WAS REPLACED AND OPERATIONAL CHECKED PER AMM 21-26-51 WITH NO DEFECTS NOTED.