REL studio III hum/rumble

I am using a REL studio III with parasound monoblocks. I am using high level inputs. The speakon
left and right are connected to each monoblocks red terminal. The ground is connected to left
monoblocks black terminal. I am using the monoblocks bi-wire posts to connect the sub.

If the amp is in standby, and the sub is switched on I get a huge rumbling sound. This rumble
does not come if the amp is switched on. Another point to note is that the rumble does not occur if the coarse cross-over is at A setting. Also the rumble gradually builds up slowly to crescendo
once the sub is switched on.

Any comments and suggestions are welcome.
not sure if this will remedy your problem, but i believe the instructions from my rel strata 3 calls for the black speakon lead to be connected to the ground of the preamp when using mono block amps. you might want to double check your manual. again, not sure if this will fix your problem.
did you try to put the negative to the chassis of your amp instead the terminal of loudspeaker's. you could have a difference of mass in between your output and the chassis. i saw the problem few time with ayre and audio research product. good luck!
I have monoblocks and a REL Storm III sub and have never had the problem you described. The only thing I do differently is hooking up both the sub and satellite speakers to the same speaker outputs on the amp. I am not sure how your amp speaker outputs are configured--I would imagine them to be in parallel, which should allow you to hook the sub inputs to the other pair of speaker posts, but perhaps not. Perhaps you should try hooking them up with both the sub and speakers hooked up to the same posts and see if there is a difference.
Ground the sub to directly on one of the screws on the amp cover, not the speaker terminal. I had the exact problem and this solved it. Good luck!
I have Parasound JC-1s with a Rel Storm III connected as you described with no problems. I would avoid any alternate connections without consulting with Parasound.

Thanks for the responses. I will look at trying out some of them this weekend and I will keep you posted.

Gandme: Are you using the JC-1's second biwire posts for the sub connection?
What is your crossover set to.
Indirstr8s, Yes I am... my crossover is set at A-4 I would have to consult the manual, but I think it is around 26 hz.
I just added a second Storm a fuller more balanced presentation.