B737 FLT CREW RECEIVES A GPWS 'TERRAIN WARNING' DURING THE ARR INTO OAK. FLT CREW EXECUTES AVOIDANCE MANEUVER.

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ORIGINALLY FILED FOR PANOCHE 2 ARR. CHANGED TO COMMO 1 ARR. CHANGED BACK TO PANOCHE 2; BUT TOLD OAK STILL LNDG RWY 11. INSTRUCTED TO CROSS BORED INTXN AT 10000 FT. ENTERED IMC AT 9500 FT. LATER CLRED TO 7000 FT; THEN 6000 FT. CLRED TO 5000 FT BTWN BUSHY AND SUNOL INTXNS. HEARD ANOTHER ACFT CLRED FOR RWY 29 APCH. CAPT REQUESTED LNDG RWY. NORCAL TOLD US RWY 29. APCHING SUNOL RADIO ALTIMETER INDICATED '2500.' AT APPROX 5100 FT; DURING LEVELOFF; GPWS WARNED 'TERRAIN; TERRAIN.' RA INDICATED APPROX 2200 FT. TERRAIN MAP SHOWED SOLID GREEN RETURNS BELOW; NO YELLOW OR RED RETURNS. INITIATED TERRAIN AVOIDANCE MANEUVER. CLBED TO 6000 FT. ADVISED NORCAL OF GPWS CLB. NORCAL STATED MVA AT OUR POS WAS 5000 FT. CHARTED MSA ON ILS RWY 29 APCH PLATE IS 5100 FT. AFTER LNDG; CAPT CALLED ATC SUPVR. SUPVR SAID NO TERRAIN IN FRONT OF US; MVA IS 5000 FT; AND THIS HAPPENS EVERY FEW MONTHS. SAID THEY HAD REVIEWED TAPES AND BOTH CTLR AND CREW HAD PERFORMED PROPERLY. SUGGESTED THAT POSSIBLE HIGH DSCNT RATE MAY HAVE CAUSED GPWS WARNING. DO NOT THINK THIS WAS THE CASE -- ACFT WAS ALREADY INITIATING LEVELOFF WHEN WARNING OCCURRED.