CRJ CREW ON AN ILS APCH AT DFW TO RWY 17C EXPERIENCE ERRONEOUS GS INDICATIONS AND PERFORM A MISSED APCH.

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DURING AN ILS APCH TO RWY 17C AT DFW WE RECEIVED ERRONEOUS GS INDICATIONS AND PERFORMED A MISSED APCH. WE WERE INITIALLY ASSIGNED 5000 FT UNTIL ESTABLISHED ON THE LOC AND CLRED FOR THE ILS APCH. ONCE ESTABLISHED ON THE APCH THE AUTOPLT PITCHED DOWN ABRUPTLY; CHASING THE GS. THE FO TURNED THE AUTOPLT OFF AND BEGAN HAND-FLYING. WE NOTICED THE PROCEEDING ACFT INFORMED THE TWR THAT THEY WERE LOW BUT SHOWING ON THE GS. BOTH THE FO AND I HEARD THIS AND THOUGHT TO GIVE THE GS EXTRA SCRUTINY. THE TWR TOLD THE PROCEEDING ACFT THAT AN AIRPLANE WAS ON TXWY Z AND THAT WAS THE REASON FOR THE GS DISCREPANCY. THE ACFT CONTINUED AND LANDED. WE NOTICED WE WERE BELOW THE PROPER GLIDE PATH APPROX AT THE FAF. THE RPTED WX WAS SCATTERED CLOUDS AT 1000 FT AND I BEGAN TO LOOK FOR THE RWY. ALSO AT THIS TIME; THE TWR CALLED US; A FEW SECONDS LATER; APCH CALLED US. I ANSWERED BOTH TIMES; BUT NEITHER OF THEM CALLED BACK. I ASKED FOR A CURRENT ALTIMETER SETTING AND WAS GIVEN THE SAME SETTING WE ALREADY HAD. THE GS ABRUPTLY WENT FULL SCALE DEFLECTION AND WE WERE NO LONGER SURE IF WE WERE ANYWHERE CLOSE TO THE PROPER GLIDE PATH; SO WE EXECUTED A MISSED APCH. WE WERE THEN VECTORED FOR AN ILS TO RWY 18R WITH AN UNEVENTFUL LNDG. WE LATER DEPARTED DFW ON RWY 17R AND WE NOTICED A LOT OF CONSTRUCTION EQUIP BTWN RWY 17R AND THE APCH LIGHTING SYS FOR RWY 17C. IT'S VERY POSSIBLE DUE TO THE CONSTRUCTION AND; MORE LIKELY; THE PRESENCE OF AN ACFT ON TXWY Z THAT WE RECEIVED MASSIVE GS SIGNAL ERRORS. SUPPLEMENTAL INFO FROM ACN 635074: WHEN WE CROSSED THE FAF WE WERE APPROX 1700 FT. THE CHART SHOWED A XING ALT OF 2275 FT. WE COMMENTED THAT WE WERE LOW; BUT ALL INDICATIONS WERE NORMAL. WE THEN EXECUTED A MISSED APCH AT LESS THAN 1000 FT BECAUSE OUR POS WAS IN DOUBT AND WE DID NOT HAVE THE FIELD VISUALLY. WE WENT AROUND AND LANDED UNEVENTFULLY ON RWY 18R. CALLBACK CONVERSATION WITH RPTR ON ACN 635073 REVEALED THE FOLLOWING INFO: CALLBACK WITH RPTR DID NOT ADD ANY NEW INFO.