I've had 2 free turbine blades depart their scene after landing which made a horrible noise/vibration above ground idle but all engine indications normal...
Once fuel was cut the prop stopped dead - bits of mashed up blade jammed the FPT. It sent an almighty shudder through the airframe and I imagine a reasonable force through the prop shaft.
Could a sudden total seizure of the FPT, with additional aerodynamic forces, result in what happened?