(I posted about this same problem a while back, but I think it's better if I cut to the updated chase in hope that someone here can help translate my technical no-how into actual know-how!)
My Prophet 6 is generating unwanted noise. I've sent it in to Thomann, but they found no fault. The noise is intermittent, and is affected by the Master Volume - if I jiggle it or push the knob upward, the noise ceases, sometimes completely, sometimes for a moment before flaring back up. Thomann replaced the Master Volume knob, just in case, I guess, and the synth seemed fine for the first week after it was returned to me. The noise, however, has flared up again. DSI has been great - they've helped me do enough troubleshooting that we're left assuming it must be some sort of ground-loop noise. My studio is such a mess and I'm so non-tech (despite being surrounded by gear, right?!), so my troubleshooting technique is more "mad scientist" than anything. Still, maybe there's simply something I can buy - an adaptor or a noise-eating bug or such. If I keep typing, I'll just make as much mess as the gear surrounding me, so I'll turn it over to anyone who might have an answer or further questions. Hope someone can help! Cheers!