I noticed the otherday that I could detect a fair vibration with the spindle anywhere between 2600RPM and 3500RPM. I took out the collet and drawbar so I could check it without any external influences and tried again. Seems there was very little difference when they were installed and the vibration was still very detectable.
Anyone else stuck their hand on the head to feel the vibrations whist at high speed?
Since you are seeing this without a draw bar I would next check if the pulleys are true.