Unexpected high vibration sgt 600gas turbine

Dear all

I face to strange behavior vibration of gas turbine.sgt 600 is double shaft gasturbie. Compressor turbine and power turbine. Compressor turbine consist two journal bearing .operational speed is about 10000 rpm for compressor turbine and 7500 rpm for power turbine. Alarm limit is 7 mm/s and the trip limit is 15 mm/s .we have just one accelerometer on the casing near the bearings for measuring and monitoring. overal vibration of both bearing of compressor turbin increase by the same about 6 mm/s and both phase of bearings around 9000 are stable so by increasing a little  rpm above 9000,for example 9100.fft of bearing number 1 have (1x,2x,3x)that have same amplitude all peaks near 5mm/s and bearing number 2 just have a 1x with 7 mm/s.by this condition machine were stable about 2 minute but suddenly vibration of bearing number 2 increase up to trip limit .my question is what cause of this behavior after 9000 rpm for bearing number 2?   

I need to mention that by checking the some part of compressor turbine by borescope  ,we find some partial touch at tip of impeller in last stage of compressor .

Pls share your idea 

Best regards

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