What was found
AFTER REACHING V1 SPEED AND BEFORE ROTATION, SEVERE VIBRATION STARTED FROM UNDERNEATH AIRCRAFT. ANTISKID INOP LIGHT FLICKERED ON FOLLOWED BY MAIN GEAR SPOILER INOP LIGHT ILLUMINATED. ANTISKID INOP LIGHT THEN EXTINGUISHED. INSPECTED AIRCRAFT FOR OBVIOUS DEFECTS, NONE NOTED. ANTISKID OPS CHECK GOOD IAW 32-43-0. BRAKES OPS CHECK GOOD BLED NR 7 AND NR 8 BRAKES AS PRECAUTIONARY PER MM 32-41-0.