My subwoofer is rumbling and popping, even with no signal at all.
I've got a Velodyne SPL-1000 II, a Denon 3805 AV/R, B&W speakers, and other components that seem unrelated to my problem.
I've hooked up the sub directly to the subwoofer line out on the 3805 using a Monster sub specialty RCA cable. The cable goes into the sub in the single input line in jack.
I've set the internal crossover to OFF and set the 3805 crossover frequency to 120Hz.
The speaker configuration setup is Subwoofer YES and it doesn't matter (for this problem) whether the other speakers are all set to SMALL or the fronts are set to LARGE and others to SMALL.
I've tried both the LFE and LFE+Main settings on Subwoofer setup.
I tried turning off the Denon and it still causes the rubbling (popping), only when the cable is physically removed does it stop.
Also, the kicker to the problem is that it is INTERMITTENT. It doesn't happen until things have warmed up. When I turn off the sub and try again later it may or may NOT rumble again.
When rumbling or not rumbling the sub seems to be working otherwise.
The kicker is that it's intermittent. If it hadn't been intermittent I'd have suggested that you had an earthing problem, but this can't be intermittent. As it is, the problem could lie with the sub, the amp or the cable. Any chance of hooking another amp to the sub or another sub to the 3805?
I don't have another sub nor another AV/R unfortunately. I'm going to try the ground loop isolator from Radio Shack today in hopes that that's it. I expect you that's what you mean by "earthing problem."