AN ACR DC-9 FO RPTS THAT HE GETS GPWS 'GS' WARNINGS WHILE SHOOTING THE BACK COURSE 4R ILS TO BTR.

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CLRED FOR LOC BACK COURSE RWY 4L AT BTR. GS SIGNALS (PRESUMABLY FROM ILS 22R) ARE RECEIVED. ON A VISUAL DAY WHEN MAINTAINING A 3 DEG GS THIS IS NO PROB. HOWEVER; WHEN SHOOTING THIS APCH IMC; AFTER STEPPING DOWN TO 720 FT AT 'LEIKO' INTXN AND THEN TO 580 FT AT DME 2.0 ICLZ LOC; ONE GOES BELOW THIS ERRONEOUS GS (AS INDICATED ON GS RECEIVER). THE GPWS THEN GIVES AN AURAL 'GS' WARNING FROM 'LEIKO' ALL THE WAY DOWN. THIS CREATES A VERY DISTURBING ANNOYANCE. THIS GS XMITTER NEEDS TO BE TURNED OFF WHEN UTILIZING LOC BACK COURSE TO 4L. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR IS FLYING A DC-9; AN OLDER ACFT. THIS MAY BE GERMANE TO THE DISCUSSION. THE GPWS 'GS' WARNING CAN BE SHUT OFF; BUT DURING THE STEP DOWN PROC; IT COMES BACK ON AGAIN AND AGAIN. THIS IS DISTRACTING TO THE CREW AND IS AUDIBLE IN THE CABIN; CREATING QUESTIONS OF CREW COMPETENCY IN THE MINDS OF THE PAX. THE RPTR COMPLAINED TO THE TWR; ASKING THEM IF THE 22R GS COULD BE TURNED OFF WHILE THE BACK COURSE 4R IS IN USE. THE TWR SUGGESTED FILING A FORM WITH THE ASRS. THE RPTR STATES THAT THIS SIT IS VERY DISTRACTING IN IMC CONDITIONS.