DC does not make a humming noise in a transformer.
First, I assume you are talking about a mechanical hum from the transformer itself and not a ground loop type hum heard through the speakers. Those two issues are considerably different.
The sin of too much DC into a transformer is that it saturates the magnetic field. Enough DC can also damage or overheat the transformer.
The far simpler and more likely explanation is that the transformer with the louder hum either has a loose lamination or a coil that is not wound tightly enough.
Is the hum audible at your listening position when no music is playing? If it is not I wouldn't worry much about it. If it is audible, I'd call the manufacturer to discuss having the amp serviced.
First, I assume you are talking about a mechanical hum from the transformer itself and not a ground loop type hum heard through the speakers. Those two issues are considerably different.
The sin of too much DC into a transformer is that it saturates the magnetic field. Enough DC can also damage or overheat the transformer.
The far simpler and more likely explanation is that the transformer with the louder hum either has a loose lamination or a coil that is not wound tightly enough.
Is the hum audible at your listening position when no music is playing? If it is not I wouldn't worry much about it. If it is audible, I'd call the manufacturer to discuss having the amp serviced.