A BE1900 FLT CREW ENCOUNTERED A TCASII TA.

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ENTERING TEX ARPT; A LONG L DOWNWIND FOR RWY 27 APPROX 5 NM W OF ARPT; TCASII INDICATED A TA. ACFT APPEARED TO BE CLBING; OPPOSITE DIRECTION; INTO OUR PATH. WE IMMEDIATELY CLBED FROM 10700 FT MSL TO 11500 FT MSL. ACFT PASSED BELOW AND TO THE R OF US. WE NEVER HAD VISUAL CONTACT. WE HAD RECEIVED NO PREVIOUS CTAF CALLS FROM THIS ACFT DEPARTING TEX. THE ONLY CTAF CALL BROADCAST HAD BEEN FROM A JET DEPARTING PRIOR TO THIS ACFT WHO HAD CLBED THROUGH OUR ALT AND ABOVE MORE THAN 5 NM AHEAD OF US. THE TA FROM THE CONFLICTING TFC APPEARED ALMOST IMMEDIATELY PRIOR TO THE WARNING AS IF THE ACFT HAD NOT PREVIOUSLY HAD ITS XPONDER ON. WE HAD MADE 3 PREVIOUS CTAF CALLS: ONE PRIOR REACHING ETL VOR; AGAIN PASSING COES VOR WHEN QUERIED BY THE PREVIOUS OUTBOUND TFC AND AGAIN AT 10 DME FROM TEX. TEX IS A BUSY ARPT WITH A GREAT DEAL OF GA TFC. FURTHERMORE; THE POPULATION IS HYPER-SENSITIVE TO NOISE FROM ACFT. CONSEQUENTLY THE ARR CORRIDOR AND DEP CORRIDOR IS THE SAME. FURTHER; THERE IS FREQUENT GLIDER TFC (SAME MOTORIZED) THAT RARELY USE THEIR XPONDERS AND COMMUNICATE ON CTAF.