What was found
ON CLIMB, RUMBLING NOISE HEARD FOR SEVERAL MINUTES, FOLLOWED BY ACRID ODOR ON FLIGHT DECK. CONTACTED F/A TO VERIFY NOTHING IN THE OVENS. DIVERTED ACFT. IN DESCENT EXTRACT FAN FAULT ANNUNCIATED, FOLLOWED QRH. LANDING WAS UNEVENTFUL. REPLACED AVIONICS EXTRACT FAN, CHECKS OK.