I have just bought a Kef Kube10b subwoofer which is attached to a Yamaha 7.1 RXV671 receiver / amp. I have Kef front, centre and surround speakers. My previous old Pinnacle subwoofer gave up the ghost and blows the 1amp slow fuse when plugged into power. Anyway, the Kef sub hums but only when connected (with audio cable) to the amp and the hum increases in volume when you increase the volume on the sub itself. I have tried; 3 different cables, run the power cable to other outlets and moved the sub away from any other electrical components. Still the same problem... After this I got a replacement new sub (as I thought this was the problem) but still humming! GRR I'm beginning to think it is the amp that has the fault, but before I spend $$$ on a new amp - any other ideas, suggestions or comments would be greatly appreciated. Thanks!