What was found
MGB WAS REPLACED DUE TO SCHEDULED OVERHAUL PERIOD COMING DUE. DURING POST MX CHECKS, HOVER & FLIGHT, OF REPLACEMENT MGB A LOW PITCH GROWLING WAS HEARD. AFTER LANDING & SHUTTING DOWN ENGS THE ROTORS WERE COASTING DOWN & GRINDING & GLUNKING COULD BE HEARD FROM THE MGB. A TECH REP & OVERHAUL SHOP TECHNICIAN INSPECTED THE MGB. THE FAN DRIVE BEARINGS WERE SUSPECTED & REPLACED WITH NEW. SUBSEQUENT RUNS & HOVER CHECK SHOWED THE SAME NOISES & ALSO HAD CHIPS ON THE MAGNETIC PLUG AFTER EACH OF SEVERAL RUNS. IT WAS DETERMINED THAT THE MGB SHOULD BE REMOVED & SENT BACK TO ABH FOR FURTHER INVESTIGATION & REPAIR. THIS ACFT REMAINS OUT OF SERVICE AT THE TIME OF THIS SUBMISSION AWAITING A SERVICEABLE MGB FOR INSTALLATION.