Just to rephrase, you get hum in both channels, and one of the channels through both speakers?
The ringing is microphonics. If it gets to you a different pair of tubes will cure it. There is a thread already about microphonics and tubes that don't have it.
Hum in the Quickie is most likely an open hot lead. Try measuring resistance from the input RCA jack center conductor to the grid of the tube. That will trace through the volume control. The resistance will probably change as the volume control is changed. Post back.
If I have your other problem right above, that is that one channel plays through both, I will have to think about it.