As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS EXPERIENCING VIBRATIONS DURING FLIGHT, MAINTENANCE WAS UNABLE TO REMOVE THE VIBRATION THROUGH TRACK AND BALANCE PROCEDURES. THE MAIN ROTOR ASSEMBLY WAS REMOVED FOR INSPECTION. DURING THE INSPECTION A TENSION-TORSION STRAP WAS FOUND CRACKED AT BOTH ENDS WHERE THE PINS HOLD THE STRAPS IN PLACE. UPON FURTHER INVESTIGATION IT WAS DISCOVERED THAT THE STRAPS INSTALLED WERE NOT THE PROPER STRAPS FOR THIS M/R HEAD CONFIGURATION.