What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: CLIMBING THROUGH FL180 AN ABRUPT VIBRATION WAS FELT IN THE FLOOR OF THE COCKPIT AND THROUGHOUT THE AIRCRAFT WITH AN ASSOCIATED VIBRATORY NOISE. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT SMF. ACCOMPLISHED AMM TASK 05-51-67 COULD NOT FIND ANY ISSUES ALSO RAN NUMBER 2 ENGINE AT IDLE TO VERIFY OIL LEAKS NO OIL LEAKS AT THIS TIME.