Looks like the interference is coming from the mede8er.
It could be a faulty circuit its funny that it does not come though the optical cable it could be something on the Coax output.
If I was you I would take it back and get a new one your unit might be faulty.
I think it is the Mede8er's power pack. It is a step-down transformer, thus it can cause the noise on the electrical circuit. But that does not mean it is faulty.
The optical doesn't generate the noise, because the optical cable doesn't conduct electricity. When the coax is connected, it completes a ground loop, thus the sub picks up the noise.
I'll see if I can find a ferrite choke to insert between the power pack and the Mede8er... Anyone know where I can buy some?