Battery voltage is 13.3 as I am plugged in and charger is working
That is nice, but it does not tell you much, other than your charger is possibly in float (trickle charge). You need to test your batteries after they have rested for 12 to 24 hours without the charger running.
Here is a copy of your Freedom manual it might help.
Sounds can be clues to a variety of issues. Buzzing can be the "Fan" as Joe suggests. It can be an electrical part beginning to fail. Or it might be a warning noise associated with the unit.
This is job for the Electrical Detective! It is that Super Hero persona all boat owners take on when something strange is buzzing that can not be ignored.