Hum
yes this is normal and it may even attract the fish. Braided Line does not make the hum that we can here and it does not give off any electrical charge associated with using the steel cable. The use of the black box will help with the electrical charge but if your zinks are set up on your boat properly you will have the proper voltage .65 for Koke's. You can check this with a voltage meter that reads 1/100 volt. Touch one lead to the wire and another to the boat ground which would be the alluminum hull or the bonding ground on a glass boat. Of course with the braided line there will be no worries about the electrical charge untill the fish is close the boat and they start to go nuts.
Good luck
Robin