What was found
IN CRUISE FLIGHT, AIRCRAFT COMMENCED AN APPROX 1/1 VERTICAL BEAT WITH AN UNUSUAL NOISE AND (HUM) IN THE AIRFRAME. PILOT DIVERTED TO FIELD LANDING SITE. AFTER SHUT-DOWN, PILOT FOUND BLADE SKIN DELAMINATING NEAR TIP. MAINTENANCE REMOVED AFFECTED BLADE AND INSTALLED SERVICEABLE MAIN ROTOR BLADE, BALANCED AND TRACKED IAW MM, OPS CHECK FLIGHT WAS GOOD.