A B757-200 EXPERIENCED BRIEF SMOKE AND FUMES AT CRUISE ALT; DECLARED AN EMER; AND DIVERTED TO AN ALTERNATE ARPT.

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CREW ARRIVED AT THE ACFT IN ZZZ1. WITH APU SUPPLYING ELECTRICITY/AIR; THE R AIR CONDITIONING PACK HAD OVERTEMP'ED (PACK RESET OK AFTER IT COOLED). R PACK OPERATING BUT STILL PUTTING OUT WARM AIR. MAINT ARRIVED AND DECIDED TO MEL THE R PACK. DISPATCH NOTIFIED FOR RE-RELEASE AND ISSUED NEW RELEASE; STATING R PACK INOP. TKOF AND CLBOUT NORMAL. AT APPROX XA45Z OVER ABC VORTAC; LEVELED OFF AT FL330. WITHIN APPROX 1 MIN; HEARD A DISTINCT THUD WITH CORRESPONDING BRIEF PUFF OF SMOKE WITH BURNING SMELL IN THE FLT DECK. (SMELL LASTED 15-30 SECONDS. ALL ENG; PRESSURIZATION; ACFT SYS NORMAL WITH NO EICAS/STATUS MESSAGES.) FLT ATTENDANTS CALLED ON INTERPHONE WITH RPT OF THE SAME THUD AND SMELL FROM AREA AROUND DOOR 2. THIS CABIN SMELL QUICKLY DISSIPATES. CAPT AND FO CONSIDERED DIVERTING AND CONCURRED THE PRUDENT AND SAFE ACTION WAS TO DECLARE AN EMER AND DIVERT TO ZZZ2. CAPT CONTACTED DISPATCH VIA RADIO TO ADVISE OF DIVERSION TO ZZZ2 AND TO RELAY TO ZZZ2 OPS. IN OUR DSCNT INTO ZZZ2 (APPROX XB05Z); HAD SECOND THUD AND BRIEF SMOKE SMELL SIMILAR TO THE FIRST OCCURRENCE. FO WAS PF. CAPT WAS PNF AND REVIEWED THE EMER CHKLIST. DUE TO ZERO PRESENCE OF SMOKE IN FLT DECK AND CABIN; CAPT DECIDED (WITH FO CONCURRENCE) THAT IT WAS MORE PRUDENT TO KEEP THE OXYGEN MASKS AT THE READY; BUT WASN'T NECESSARY TO DON THE EQUIP. EVERYTHING CHKED OUT NORMAL AND WE TAXIED TO GATE. MAINT REPLACED R RECIRCULATION FAN AND SOME FILTERS (NO OBVIOUS DAMAGE).