What was found
BURNING METAL SMELL FROM CENTER OF AIRCRAFT. ONCE RECIRC FANS TURNED OFF, SMELL BEGAN TO DISSIPATE. NO EICAS MESSAGES DURING EVENT, SMELL SUDDENLY CAME TO THE ATTENTION OF BOTH FLIGHT ATTENDANTS AND THEN PASSENGERS. DECLARED EMERGENCY, DIVERTED TO LGA, LANDED WITHOUT INCIDENT. R&R RT RECIRC FAN IAW AMM 21-24-01.