I received my MK-330 charger but don't have my new boat yet so I figured I would just hook up the charger to my old boat batteries and 1 from my tractor to try it out. 2 banks said charged which I expected and 1 bank went on charge, after about a half hour the charger was buzzing pretty loudly, is this normal? It was only charging on 1 bank at 10 amps and it was way louder than I expected, if all 3 banks were running and each of them sounded like that.....well lets just say not what I expected. If this is normal that's ok, I just want to make sure. I think I will switch the batteries around an verify if each bank sounds like that. I hope it's normal as return shipping charges will eat up the rebate they have going. Thanks for the help.