What was found
APROX 2 HOURS AFTER T/O BOTH PILOTS NOTICED A RUMBLE AND VIBRATION OCCURRING EVERY 30 TO 45 SECONDS LASTING FOR ABOUT 3 SECONDS. THE RADAR WAS ON AND IN THE AUTO POSITION. THE RUMBLE & VIBRATION QUIT WHEN RADAR WAS TURNED OFF. AFTER 5 MIN WAIT WE TURNED THE RADAR BACK ON AND RUMBLE CAME BACK. TURNED RADAR BACK OFF AND RUMBLE STOPPED. GROUNDED - YES. WXR OPERATIONAL TEST DONE REF AMM 34-43-00-710-802-001: SLIGHT VIBRATIONS IN FLIGHT DECK FLOORBOARDS WHEN TEST BUTTON PRESSED. WXR ANTENNA DRIVE UNIT REMOVED AND REPLACED REF AMM 34-43-11. OPERATIONAL TEST DONE SUCCESSFULLY WITH NO VIBRATIONS NOTED.