So since the EVO 300 has all RCA ins and outs, I'm assuming all equipment is connected via RCA cables. Correct?
Disconnect the internet/tv cable from the cable box or/and modem.
Still waiting to hear from you if this made a difference. To be clear, disconnect the coax cable from the cable company, so it makes no connection to your modem or cable box.
Looking on the back of the OneR's, I can't tell if there's 3 prongs in the AC socket or just two? I think it's two, but please correct me if I'm wrong.
Is it safe to assume the OneR's still reproduce sound if they aren't powered (ie, plugged into an outlet)? I understand the sub sections of them will not work, but does the rest of the speaker system work? If they still reproduce audio without the subs functioning, is the hum still there? Also, just try unplugging power to one of them, and see if that changes anything.