What was found
ON APPROACH, WITH THE GEAR UP AND THE FLAPS AT 5, OBSERVED PWS FAIL ON BOTH NAV DISPLAYS ACCOMPANIED BY A LOUD LOW FREQUENCY RUMBLING VIBRATION IN THE RADOME/NOSE GEAR AREA. THIS CONTINUED THROUGH GEAR EXTENSION, LANDING AND TAXI. AND CONTINUED WHILE PARKED WAITING FOR GATE. NOISE SUBSIDED ON FINAL TAXI IN TO THE GATE ABOUT 10 MINUTES AFTER LANDING. GROUNDED - YES. REPLACED WX RADAR DRIVE UNIT REF B737-800 AMM 34-43-11/401. PRECAUTIONARY, REPLACED WX RADAR R/T UNIT REF AMM 34-43-41/401. ACCOMPLISHED OPERATIONAL TEST OF WX RADAR SYSTEM, TEST PASSES. ETOPS GROUND VERIFICATION SUCCESSFUL. REF AMM 34-43-00/501. AIRCRAFT RELEASED FROM MEL 34-15D.