Paradigm PS1000 subwoofer problem

[Dragoh]

The sub rumbles when there is no signal feeding it. It should automaticaly activate (like most subs) when it recieves a signal but as soon as i connect the phono cable it switches on and starts. I recently changed my amp from a Denon AVCA10se to an Onkyo 875 and as far as i can remember it worked fine with the Denon. To be honest i cant see how the change in amp would cause this problem.

So long as the phono cable is connected at the sub it continues to rumble. Whether the amp is on/off, or the phono cable is disconnected from the amp. I have tried the sub in different mains points and with different phono cables/mains leads, all to no avail. I even disconnected all the AV equipment from the mains.

As a temporary measure i am now using an old JPW sub and this works fine connected with the same cable (Black Rhodium sub cable) and its plugged into the same mains block. The only difference with the mains supply is the JPW has a pre-connected mains lead and the Paradigm uses the more conventional push-in mains lead. (The JPW can't match the Paradigm for performance).

Thats about as much info that i can think of. Has anyone got any ideas? I kind of think its a service job though