My supernova 12" earthquake subs are suppose to shut off when no-signalis detected after 30 minutes or so, when the receiver (Yamaha RXV-1400) is on, but no source output, the subs go into stand-by, like they should, but if I shut the whole system down, the subs "greenlight" the entire time and have a hum, I am using a shielded sub-cable of decent quality, any suggestions??

Sunfire amps & processor Sammy 50" Crown amp 2-SVS SS Maple Ultras, Axiom 60s,22s,150cc, QS8s