What was found
AIR TURNBACK, FLT 7 DIVERTED AS CREW PRECAUTION DUE TO VIBRATION IN CRUISE AT 1.7 THRU CLIMB FL 360-380 N1 VIBRATION LT ENGINE. CLIMBING TO 3.9 REDUCED POWER STABLE AT 1.5 IN TURN CLIMBED TO 1.7, TROUBLESHOT IAW TSM 77-00-00-810-814-A22. VIBRATION DUE TO FAN LUBE AND WITHIN LIMITS.