I've got a bit of a problem with my weird noise pedal; The Great Destroyer from Dwarfcraft.

I built the pedal from a kit and it's a crazy beast, making all sorts of weird noises but built around the basic premise of a fuzz pedal. One of the side effects of its weirdness is that it has a strange sputtering out noise when the signal level drops; ie after you sustain a note for a few seconds. I figured I could discourage this by putting the pedal in the FX loop of my HD500 at line level. However, the result was not what I expected.

I put the TGD in the loop, switched it on, then filled one of the empty spaces in my patch with the FX Loop. As soon as I did that, there was a constant loud noise from my monitors, even though the FX Loop was switched off. If I take the Loop out of the patch, the noise stops immediately, but with the Loop in the patch, regardless of whether or not it is switched on, the noise is there. If I turn the TGD off, the noise stops immediately.

I fetched my Dad round to have a look, as he's a retired electrical engineer, and we agree that it's not earth-related, as the HD500's ground lift makes no difference (and yes, I'm using XLRs) and there's nothing else plugged into the HD500 other than the TGD, so the whole system has a single earth reference through the TGD's power supply; a brand new Harley Benton Powerplant which currently only powers the TGD. And it can't be signal-related, as it makes the noise with the Loop disengaged.

My Dad reckons it sounds more like an overload kind of noise (he described it as sounding a bit like a chopped square wave), but I've tried the Loop on both Line and Stomp and, while the timbre of the noise changes, it's amplitude does not.

I realise this is (more than likely) a problem with the TGD and not the HD500, but do any of you more electonically-minded folk out there have any idea what process is creating the noise and how/why it is getting into the signal chain, even with the FX Loop switched off? I'm baffled.

Thanks.