Yup, that's a Magnatek 6300.. The hum is the transformer in the converter which is behind the fuse/breaker panel.
Now the bad news.. This is an old single stage unit, you need to check your batteries and may need to disconnect them to prevent overcharging,, This unit is well known for boiling batteries dry and damaging them.. A upgrade to a good 3-stage or 3-stage plus converter is highly recommended..
Some of the better converters:
Progressive Dynamics 9200 series
Progressive Dnamics 9100 with the optional charge wizard (The difference in those two is the 9200 the wizard is not an optin, it's built in)
IOTA with IQ-4
Xantrex True Charge
I am biased toward the Progressive Dynamics myself.. but note that is a bias.. That said, in researching converters it is among the best.. So Ranks right up there with the rest of those I listed.
BestConverter - Converters, Inverters, Electrical Supplies, Electronics
Has both information on upgrading (Scroll down to the "Extra Info" frame) and good prices on the upgrade.. They also have an upgrade kit that makes it easier.