LTT FO; PF; LOSES SIGHT OF TFC SIGHTED DURING VISUAL APCH PROC AND EXECUTES A HDG TRACK DEV IN REMAINDER OF APCH; ENCOUNTERING A TCASII RA ENRTE.

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I WAS THE PF FROM MYR TO RDU. WE HAD A HIGH PITCH SQUEELING SOUND AT 4.5 PSI AT 10000 FT AT CRUISE. THE CAPT WAS ON COM #2 TALKING TO MAINT WHILE I CHKED IN WITH RDU APCH. I WAS TOLD TO EXPECT RWY 23L AND GIVEN A FREQ CHANGE. I WAS WAITING FOR A BREAK IN FREQ CONGESTION ON THE NEW FREQ WHEN THE CAPT SAID HE WAS BACK ON COM #1. HE CHKED IN AND WE WERE CLRED TO 6000 FT. WE WERE THEN CLRED TO 4000 FT AND GIVEN A HDG OF 320 DEGS. AN MLG AT 10:30 - 11 O'CLOCK POS ON A R BASE TO RWY 23R WAS POINTED OUT AND OUR RWY WAS SWITCHED TO RWY 23R. THE CAPT RPTED THE MLG IN SIGHT AND WE WERE CLRED FOR THE VISUAL APCH TO RWY 23R AND TOLD TO MAINTAIN VISUAL CONTACT WITH THE MLG. THEN ANOTHER VOICE ON RDU APCH SAID 'YOU CAN DSND FROM 4000 FT TO 2000 FT IF YOU WANT.' THIS NONSTANDARD TERMINOLOGY MADE ME WONDER WHY; IF IN FACT WE WERE ALREADY CLRED FOR THE VISUAL APCH; WERE WE GIVEN A NEW ALT. IT SOUNDED LIKE THERE WAS SOME CONFUSION IN THIS VOICE AND THERE WAS POSSIBLY MORE THAN 1 CTLR ON THIS FREQ. AT THIS TIME I LOST VISUAL CONTACT WITH THE MLG SO I FLEW THROUGH FINAL TO AVOID A POTENTIAL MIDAIR COLLISION WITH THE MLG. I ATTEMPTED TO TELL THE CAPT I HAD LOST SIGHT OF THE MLG WHEN THE CAPT TOLD ME HE HAD LOST SIGHT OF OUR TFC. THERE WAS A HAZE LAYER AT OUR ALT WHILE LOOKING TO THE W INTO THE SUN. THE CAPT WAS UNABLE TO NOTIFY ATC THAT WE HAD LOST SIGHT OF THE TFC BECAUSE THERE WAS SOME FREQ CONGESTION. I NOTICED A WDB AT 12 O'CLOCK AND 3 MI THAT APPEARED TO BE AT 4000 FT. I INCREASED MY DSCNT RATE THROUGH 3000 FT AND TURNED BACK TOWARD FINAL. THEN WE RECEIVED AN RA ON THE TCASII. THE TCASII ADVISORY COMMANDED A DSCNT SO I FURTHER INCREASED MY DSCNT; THEN THE CLR OF CONFLICT VOICE CAME ON. DURING THIS TIME THE CAPT WAS UNABLE TO ADVISE ATC THAT WE HAD LOST SIGHT OF THE MLG BECAUSE ATC WAS ADVISING US OF THE WDB TFC. ATC FOLLOWED BY GIVING THE WDB ALTERNATE INSTRUCTIONS TO INCREASE THE SPACE BTWN US. THIS WDB HAD PREVIOUSLY BEEN CLRED TO FOLLOW US ON A VISUAL TO RWY 23R. I MADE A NORMAL LNDG AND EXITED THE RWY AS EXPEDITIOUSLY AS POSSIBLE. THE WDB ALSO MADE A NORMAL LNDG. FREQ CONGESTION; ATC POS CHANGE; BACKGND NOISE CREATED BY COM #2; GLARING SUN AND HAZE ON FINAL; DIFFERENT TYPES OF HEAD SETS AND MICROPHONES; FATIGUE CREATED BY 4 DAYS OF FLYING; WAKE TURB; POS OF GS ANTENNA ON AN MLG; ARE ALL CONTRIBUTING FACTORS. THIS SIT INVOLVED MANY HUMAN AND MECHANICAL FACTORS THAT ARE AFFECTED BY MANY VARIABLES. I BELIEVE THAT THE TCASII IS THE MAJOR FACTOR THAT PREVENTED A NEAR MISS.