ACR X RECEIVED GPWS UNAUTHORIZED CLB FROM ASSIGNED ALT. PLTDEV. ACFT EQUIP PROBLEM FALSE GPWS.

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ACR X ON DSCNT INTO PSP. WE PLANNED ON LNDG RWY 30 BUT IT WAS SWITCHED TO RWY 16 AND WE WERE GIVEN A CLRNC DIRECT TO PSP VOR AND A CLRNC TO 7000 FT. PRIOR TO DSCNT WE CHKED THE TERMINAL ARR CHART AND DETERMINED HIGHEST TERRAIN TO BE 8000 FT NE 7500 E DROPPING RAPIDLY IN THE VALLEY SE OF PSP TOWARDS THERMAL. IN ACCEPTING THIS CLRNC WE KNEW OUR POS CLOSELY APPROXIMATED THE VICTOR AIRWAY AND BASED ON THAT ACCEPTED THAT ALT AS A MVA. WE WERE SURPRISED AND STARTLED TO RECEIVE A TERRAIN WARNING. WE IMMEDIATELY INITIATED A PULL UP UNTIL THE WARNING STOPPED WHILE INFORMING ATC OF OUR MANEUVER; AS SOON AS THE CURRENT XMISSION STOPPED WITH ANOTHER ACFT; BY WHICH TIME WE CLBED TO 8000 FT. ATC ASKED ABOUT OUR FLT CONDITIONS AND THE FO REPLIED THAT WE WERE ON TOP AND HAD BEEN IN THE CLOUDS. WE WERE GIVEN ANOTHER DSCNT CLRNC AFTER THE CTLR EXPLAINED THAT THE PEAK THAT HAD GIVEN US THE WARNING WAS 3 MI TO THE SIDE. WE HAD APPARENTLY GOTTEN THE WARNING BASED ON CLOSURE RATE AND PROX TO TERRAIN. IN TALKING TO THE CTLR ON THE TELEPHONE AFTER LNDG HE SAID THAT ONLY OUR COMPANY EQUIP SEEMS TO GIVE THESE WARNINGS IN THIS AREA; AS IF OUR EQUIP MAY BE CALIBRATED DIFFERENTLY OR MADE BY A DIFFERENT MANUFACTURER.