As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT MADE A PRECAUTIONARY LANDING AFTER NOTING AN INCREASING MAIN ROTOR VIBRATION. AMTS DISCOVERED THE HARDWARE LOOSE SECURING THE YELLOW MRB S/N 3407 DAMPER STAY ASSEMBLY. DETAILED INSPECTION OF THE MRB AND AIRFRAME WAS PERFORMED AND ATTACHMENT HARDWARE WAS REPLACED. VIBRATION CHECK WAS PERFORMED UTILIZING APPLICABLE VIBRATION ANALYSIS INSTRUMENT.