NO COCKPIT WARNING OF APU FIRE.

Narrative

AFTER PUSHBACK AND ENG START; FLT ATTENDANT IN REAR RPTED LOUD BANGING NOISE. CAPT WENT TO LISTEN AND DECIDED TO RETURN TO GATE. AFTER RETURN TO GATE; RAMP AND GND RPTED FIRE IN TAIL PIPE OF APU. GND MECH ASKED US TO RESTART APU TO 'BLOW OUT' FIRE. FIRE TRUCKS AND GND PERSONNEL WERE ATTEMPTING TO PUT OUT THE FIRE; UNKNOWN TO US IN THE COCKPIT. THERE WERE NO COCKPIT INDICATIONS OF FIRE IN THE APU. SHOULD HAVE HAD INDICATION ON ECAM AND/OR FIRE LIGHT. THERE WAS A DANGER TO GND PERSONNEL AFTER RESTART WHILE THEY WERE TRYING TO PUT OUT FIRE. THERE WAS POOR COM BTWN RAMP CTL AND GND MECHS AND COCKPIT. I THINK WE NEED TO KNOW WHY THERE WAS NO COCKPIT INDICATION OF FIRE; ALSO THERE HAS BEEN 1 PREVIOUS RECORD OF TAILPIPE FIRES IN AIRBUS APU'S OR COMPRESSOR STALLS OF THAT NATURE. I THINK AS AIRCREWS WE NEED MORE INFO ON THIS PROB. THERE WAS NO DAMAGE TO THE APU AFTER MAINT INSPECTION. THIS ISN'T A COMMON A-320 PROB. SHOULDN'T' THERE BE AN ECAM WARNING? WE COULD NOT HEAR THE COMPRESSOR STALL FROM THE COCKPIT EITHER.