I sent 2 new cranks out to texas to get trued up he is going to send them back to me by monday and if all goes well i will post up his contact info heres a pic of his setup with my cranks..
the simple answer is torsional vibration and natural frequency.Can you ask the crank truing person why a crank would only cause vibration between 24 and 28mph? From 28 to 34mph there's no vibration. weird!