I'm stumped with a pedal mystery, and I was hoping the many gear gurus on this board could help me out. Let me say in advance I'm thankful for any help that will be offered. I've built up a couple of pedalboards in the last few months, and one finishing touch I wanted was a true bypass looper so that I could activate different groups of pedals with just a click or two rather than several. After reading several reviews, I ordered a couple of loopers from Loop-Master. Brian at Loop-Master is great to deal with, and he had my custom pedals delivered in a very reasonable time at a fair cost. I set up the boards, and things seemed to be going swimmingly. On my "main" board, I have a Wah, Volume, Keeley Comp, Keeley BD-2, OCD, and H20 with everything post Volume Pedal going in through the looper (Comp, BD2, OCD, and H20). I noticed a few days after that when I cranked the controls on the BD2 (just to see how nasty it could get) that it would get this nasty squeal. The squeal would oscillate depending on how I turned the controls (including tone, level, and distortion). Turning the guitar's volume knob would control the pitch/volume of the squeal as well. So, I tried to narrow down the culprit. I noticed that I would NOT get the squeal when it was just the guitar plugged into the BD2 and then into the amp. It would feedback Nugent/Hendrix style, but it wouldn't have this weird squeal. However, if I plugged the BD2 into the true bypass looper, then it would squeal when turned up. I tried eliminating various components. I tried different cables, amps, guitars, batteries, and power supplies. At first I thought it might be the BD2/Loop-Master combo, but I tried a Keeley DS-1 with Keeley Comp, a Visual Sound Jeckyll and Hyde, and the OCD, and I would get the squeal from them as well. Every time, the one constant was the Loop-Master looper. Well, this depressed the heck out of me because Brian's loopers are really cool and obviously very useful. Still, I thought the units must have been defective. I contacted Brian and he offered to let me send the back so he could check them out. I never did that because I wanted to try some other true bypass loopers. I ordered the Keeley model (the Japanese apartment) and, sure enough, the squeal was still there. Guitar into cranked overdrive into amp=wild feedback. Guitar into Overdrive (in the loop pedal) into amp=nasty squeal. I thought "what the heck?" and tried yet another true-bypass loop pedal, the Radial Bigshot EFX. Yes, the squeal is still there. Obviously, these loop pedals are not all defective, but I'm stlll clueless about what's causing this issue. I'm not an electronics genius by any stretch, and I sure as heck couldn't (and can't) figure out what would cause one of these pedals to squeal like this. I have tried to replace every variable I can think of. I typically use George L cables, but I've tried other brands, and the squeal is there. I've tried six electric guitars, three different amps, and it just doesn't matter. I've tried batteries and power supplies, and it doesn't make a difference. I'm stumped. Is there anything about a True Bypass Loop pedal that would cause this behavior with Overdrive/Distortion pedals? There are people on this board that know a lot more than I do about such things. Please, help me figure out what the heck is going on here. I'm also curious if anyone has had similar experiences. For all I know, this behavior is normal. However, it's not one particular looper or one particular overdrive. Are there variables I haven't considered? Thanks, everyone!