B737-300 CREW HAD SUSPECTED ENG FAN BLADE ICING THAT WAS DETECTED ON THE VIBRATION MONITOR.

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WX WAS IFR; TEMP 18 DEGS F; VISIBILITY 1 MI. AFTER REMOTE DEICED; TOOK RWY 34 FOR TKOF. PERFORMED ENG RUNUP ON RWY. NOTICED INITIALLY #2 ENG VIBRATION HIGHER THAN NORMAL (3.0). AFTER A FEW SECONDS; RETURNED TO MORE NORMAL VALUE (1.5). ALL OTHER ENG PARAMETERS COMPLETELY NORMAL. AFTER RUNUP; COMMENCED TKOF AND EVERYTHING WAS NORMAL UNTIL 10000 FT. #2 ENG WENT ABOVE 4.0 ON VIBRATION. I SUSPECTED ENG ICE AND PERFORMED ICE SHEDDING PROC (45% THEN TO 80%) AND RAN HIGH VIBRATION IRREGULAR PROC FOR ENG ICE. ENG IMMEDIATELY RETURNED TO NORMAL VALUE (1.5). WE CONTINUED TO CRUISE AND ENG WAS NORMAL UNTIL DSCNT. ON DSCNT TO PHL; WHENEVER ENG THRUST CHANGED (RETARDED OR ADVANCED); VIBRATION WOULD GO INITIALLY TO AROUND 3.0; THEN RETURN AGAIN TO 1.5 OR SO. NOW WONDERED IF WE HAD SOMETHING MORE THAN AN ICE PROB; AS NO ICING CONDITIONS EXISTED INTO PHL. MADE A LOG ENTRY AND DISCUSSED WITH MAINT ON ARR. NEXT DAY; FOUND OUT ENG HAD ROTOR BLADE WARPING. I BELIEVE WE DID EVERYTHING CORRECTLY. MAYBE SHOULD HAVE RETARDED THROTTLES TO IDLE ON RUNUP AND TRIED RUNUP SECOND TIME; BUT AT TIME; DID NOT SEEM NECESSARY AS ENG VIBRATION RETURNED TO NORMAL VALUE DURING RUNUP.