CORP MLG HAS GPWS ALERT WHEN DSNDING ON RADAR VECTORS IN IMC.

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DSNDING TO VNY FOR THE VOR-A APCH FROM THE NE. WE CROSS OVER A MOUNTAIN RANGE (OAT MOUNTAIN) APPROX 5 MI N AND RUNNING PARALLEL TO OUR APCH COURSE. WE ARE TURNED SSE TO CROSS MOUNTAINS AND BE ON BASE LEG FOR THE APCH. THE GPWS SOUNDS TERRAIN AND PULL UP JUST AS WE RECEIVE THE INTERCEPT VECTOR. WE INITIATED AN IMMEDIATE CLB TO APPROX 4500 FT WHERE THE GPWS STOPPED ALARMING. SOCAL APCH ADVISED US THAT THE MVA FOR THE AREA WAS 3500 FT MSL. WE ADVISED THEM THAT IMC WHEN THE VOICE SAYS PULL UP WE DO WHAT HE SAYS. WE CONTINUED OUR APCH FROM THERE AND LANDED. WHILE I WAS PRETTY SURE THE ALERT WAS FALSE; WHEN YOU ARE IN THE CLOUDS IT CAN BE VERY DISCONCERTING. THIS APPROX POS HAS BEEN THE SITE OF AT LEAST 3 OTHER FALSE GPWS WARNINGS IN THE PAST IN THIS ACFT. I THINK IT IS POSSIBLE THAT THERE IS A FAULT IN OUR GPWS OR THAT THE MOUNTAIN RANGE THAT WE FLEW OVER MAY CONTAIN SOME RADIO EQUIP THAT INTERFERES WITH THE RADAR ALTIMETER FOR THE GPWS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT HIS COMPANY DOES NOT CHOOSE TO CHK OUT THEIR EQUIP SO HE HAS NO IDEA IF THAT IS THE PROB. THE MOUNTAIN OVER WHICH THEY FLY ON THIS APCH HAS A GREAT AMOUNT OF RADIO FACILITIES ON IT AND HE FEELS THIS MAY BE THE PROB. BOTH PLTS HAVE HAD SUCH WARNINGS IN THE PAST BUT ALWAYS IN VFR. THIS ONE SHOOK UP RPTR BECAUSE IT WAS IMC. IN THE VFR CONDITIONS THEY DID NOT RESPOND BUT CONTINUED FLT AND IT WAS A LONG TIME BEFORE THE WARNING STOPPED; QUITE A DISTANCE FROM WHERE THEY CLRED THE TERRAIN. THE TERRAIN DOES RISE RATHER FAST UP TO 4000 FT IN FAIRLY CLOSE PROX TO THE ARPT. BOTH PLTS HAD JUST COMPLETED SCHOOL AND HAD BEEN GIVEN SEVERAL GPWS SITS DUE TO THE ACCIDENT IN S AMERICA. THIS WAS JUST LIKE THE SIMULATED EXPERIENCES; ONLY REAL.