Hi. Advice needed please. I have bought a Yamaha DSP-AX750SE amplifier (new) and a set of Castle Compact 5.1 home cinema speakers (a few months old from a hifi retailer on ebay). My problem is that when I switch the amplifier onto 'standby' mode the Castle Compact Cube (the subwoofer), after a short delay, gives out a quite loud, really annoying hum. It also hums to a lesser extent when the music fed into the amplifier is stopped. If I turn on the subwoofer without it being connected to the amplifier, then is doesn't hum at all. Is there likely to be a fault with either the amplifier or subwoofer that might need repair. Otherwise, does anyone have a solution for a cure? Thank you.