What was found
UPON CLEARANCE FOR TAKEOFF, ADVANCED THRUST LEVER T/O CONFIG WARNING HORN SOUNDED (REF - SPEEDBRAKE WAS STOWED, TRIM SET FLAPS WERE 15 - 15 GREEN). CLEANED FLAP WARNING SWITCH CYCLED FLAPS TO 15 DEG. OPS CK GOOD. NO HORN AND RESET FLAPS TO 0 DEG.