A FOKKER 100 ON INITIAL CLB AT 500 FT DIVERTED DUE TO HIGH N2 VIBRATION INDICATION ON #1 ENG SUSPECTED TO BE CAUSED BY THE N2 VIBRATION SENSOR.

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ABOUT 500 FT INTO OUR CLB OFF AUS WE RECEIVED AN ENG #1 N2 VIBRATION HIGH WARNING ON MFDU AND ENG VIBRATION INDICATOR. WE CLEANED UP AND REDUCED PWR ON SCHEDULE. WHEN PWR WAS REDUCED; N2 INDICATION AND MFDU CHKLIST TITLE RETURNED TO NORMAL COLORS; WHILE N2 REMAINED VERY HIGH; BUT GREEN. SELECTING ALTERNATE VIBRATION OR ENG ANTI-ICE ON HAD NO EFFECT ON THE HIGH N2 INDICATION. WHEN TALKING TO THE #2 FLT ATTENDANT; HE NOTED A LOUD ABNORMAL GROAN FROM THE L ENG JUST AFTER TKOF. WE RETURNED TO AUS AS A PRECAUTION UNDER NORMAL CONDITIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT AFTER RETURNING TO AUS; MAINT INSPECTED THE ENG FOR ANY OBVIOUS FAULTS BUT DID NOT CHANGE ANY PARTS. THE RPTR SAID MAINT WAS OF THE OPINION THE PROB WAS THE #1 ENG N2 VIBRATION SENSOR. THE RPTR SAID MAINT DECIDED TO MAINT FERRY THE ACFT TO ZZZ FOR A MORE INTENSIVE INSPECTION. THE RPTR STATED THE ACFT WAS FERRIED BY THE RPTR AND COPLT AND DURING TKOF AND CLB COULD NOT DUPLICATE THE HIGH N2 INDICATION ON #1 ENG.