AN ACR FK10 FLC GOT A GPWS TERRAIN WARNING WHILE DSNDING OUT OF 8300 FT OVER TERRAIN THAT PEAKED AT 1395 FT TO 1602 FT IN THIS GENERAL AREA. ACFT IN RAIN AT THE TIME.

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APPROX 30 NM SE OF RST AIRFIELD WHILE DSNDING OUT OF 9000 FT FOR 4000 FT AT ABOUT 8300 FT RECEIVED A GPWS OF TOO LOW TERRAIN. STOPPED FURTHER DSCNT AND CLBED IMMEDIATELY TO 9000 FT. NOTIFIED ATC AND SUBSEQUENTLY COMPLETED APCH TO RST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THAT AT THE TIME HE HAD ENTERED A STEEPER THAN NORMAL DSCNT OF ABOUT 3000 FPM WITH A DECK ANGLE OF ABOUT 5 DEGS NOSE DOWN AND IT WAS ALSO RAINING HEAVILY. HE SAID THAT HE KNEW THE TERRAIN IN THE AREA AND HE KNEW THAT THE GPWS 'TERRAIN' WARNING WAS CERTAINLY FALSE; BUT REACTED PRIMARILY AS A TRAINING RESPONSE. HE SAID THAT AFTER INFORMING THE APCH CTLR AND XCHKING THE UNDERLYING TERRAIN ELEVATION WITH THE CTLR; THE FLC WERE ABLE TO CONTINUE THE APCH WITH NO PROB. THEY ENTERED THE DISCREPANCY INTO THE MAINT LOG. AFTER REVIEWING THE WRITE UP WITH THE MAINT PERSONNEL AT RST AND CONFIRMING THAT THE GPWS SYS WAS; APPARENTLY; NOW FUNCTIONING THE FLC WENT TO THEIR NEXT STATION WHERE THEY CHANGED TO ANOTHER ACFT. THEY BRIEFED THE FLC THAT TOOK THIS ACFT ABOUT THE RST INCIDENT. THE ONCOMING CAPT ASKED IF THEY WERE IN HVY RAIN AT THE TIME OF THE GPWS WARNING; ACCORDING TO THE RPTR. WHEN THE RPTR RESPONDED AFFIRMATIVELY THE OTHER CAPT; APPARENTLY; SAID THAT HE HAS HAD THIS SAME TYPE OF FALSE WARNING HAPPEN TO HIM IN HVY RAIN SEVERAL TIMES AND THAT IT IS A CHARACTERISTIC OF THIS INSTALLATION ON THE FK10. THE OTHER CAPT HAS; ALLEGEDLY; FLOWN OTHER ADVANCED ACFT; BUT ONLY ON THIS ACFT HAS HE NOTED THIS PARTICULAR PHENOMENON. THE RPTR HAD JUST FLOWN THE B727 AND WAS NEW TO THE FK10.