A321 FLT CREW EXPERIENCES OSCILLATING ROLLS TO THE L AND R DURING APCH TO PIT.

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THIS WAS ABOUT 4 1/2 HRS AFTER COLD FRONT PASSAGE INTO PIT. ON DSCNT BELOW 12000 FT WE HAD BOTH ENG AND WING HEAT ON. FO FLEW A COUPLED APCH TO RWY 28L. JUST INSIDE THE FAF; I SECURED THE WING HEAT AS WE WERE NOW IN VMC. I CALLED OUT VREF +20 KTS AT 500 FT WITH ACFT STABILIZED IN BREEZY CONDITIONS. ABOUT 400 FT; THE L WING DIPPED DOWN; FOLLOWED BY A ROLL TO THE R. THE FO DISCONNECTED THE AUTOPLT AND THE ACFT CONTINUED TO ROLL BACK AND FORTH. BY 200 FT; THE DECISION WAS MADE TO GO AROUND. AS SOON AS THE THRUST CAME UP TO TOGA; THE ACFT FLEW NORMALLY. THE GAR WAS FLOWN NORMALLY AND WE DECIDED TO FLY THE NEXT APCH AT CONFIGN 3 VERSUS FULL FLAPS THAT WE HAD JUST DONE. AT FIRST WE FLEW THE CONFIGN FULL BECAUSE IT WAS A WINDY EVENING; BUT NO RPTS OF WINDSHEAR WERE HEARD BY US. WE RECEIVED NO WINDSHEAR CAUTIONS OR WARNINGS BY THE ACFT WINDSHEAR PREDICTION AND DETECTION SYS (SECOND APCH AND LNDG NORMAL). WE HAVE A CONFIGN 3 POLICY WITH MODERATE TO SEVERE ICING. WE HAD ABOUT 1/4 INCH OF MIXED ICING ON THE FIRST APCH WHICH I WOULD CALL LIGHT TO MODERATE. I BELIEVE THE ROLLS MAY HAVE BEEN CAUSED BY A COMBINATION OF WIND AND LIGHT TO MODERATE ICING AND WILL USE ONLY CONFIGN 3 IN THE FUTURE WITH SIMILAR CONDITIONS.