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Thanks for everyone's comments. I think there is clearly a radial shaft resonance in the high vibration area, but I still don't understand the sub-synchronous vibration that occurs at the same time. I am wondering if the rubber mounting of the outer race of the bearing is at play here.

No data from a controled rundown; unpowered coast down shows high vibes in the same frequency range, but the rate of speed change is so fast, it is difficult to see what is really happening.

On a high speed, well balanced rotor, when running up in speed, there is a speed where vibrations start to increase significantly. At this point, increasing the power does not increase rpm very much, but does increase vibration. After considerable increase in power and subsequent slight...