My sub is humming (electrical sort of hum!) It's a Gale 300 10" Active sub. I'm using a single good-ish quality 10m phono lead from my Amp (Yamaha DSP-A592) to a phono input on the back of the sub. I've put a magnetic shield device (designed to stop this sort of thing) around the mains cable, but it hasn't made the slightest difference. If I remove the phono lead from the sub, the noise stops. So am I right in thinking the Amp or lead is at fault? Can anyone suggest a simple test I can do: 1) to eliminate the cause 2) without blowing up the sub! Many thanks Pete.