384 voltage variation

This issue started on Tuesday. The starter sounded funny then wouldn’t start. Check the batteries and three of the four needed replacing. Replaced all four and cleaned all the straps. Started like a champ, made a little buzzing sound though and some clacking noises. The next morning I got about 100 yards and it sounded her Renda‘s. Parked it, pulled the starter, it was tore up. Had a new starter installed. Noticed on the gauge, and my CB gauge, voltage was jumping all over the place. Would drop as low as 9.9. For ####s and giggles, replace the alternator. Alternator reads 14.5 on a multi meter. Batteries are 13.9. Bolted still fluctuating.