You could be right about this.
But maybe your dc blocker was not removing enough dc volts?
Some only removes 0.5 volts. Others removes up to several volts.
If you have dc 2 volts and use a dc blocker that removes 1 volt you will notice a difference. But the hum only gets lower .
This is possible to measure and build a blocker that is strong enough.
I'm not shore about hove much the one I linked to removes. But I think I did read somewhere it is in the range of somewhere between 2 and 4 volts.
It's easy to calculate if you have the skills, I don't.
In my case in an acoustic treated (quiet)room I could hear the hum from 4 meters. Of course the noise was depending on howe mutch dc it was at the moment. But worst case cenario 4 meters.
With the dc blocker it's always quiet. Or the truth, if I put my ear dawn on the top of amplifier and the room is totally quiet I might sometimes hear it. But that is good enough. Tommy