Ever thought it could be the clutch bell hitting the flywheel? or like AMG said, the clutch bell bushes overheating, expanding, and effectively engaging the clutch bell at a very low rpm.
It would be very unlikley that a high idle would cause it... a high idle, even high enough to engauge the clutch, would not allow the car to sit still.
My money is on the clutchbell bushes.... a flame out because of engine tune, doesnt produce the sound that has been described.