I just bought a used Mesa Recto recording preamp and I really love how the thing sounds, compared to my previous Engl E530 preamp, but I have a technical issue. When I use just a little bit more aggresive settings on the chorus, delay and reverb in my pedal board (connected to the loop), I strum a chord, or just a single note, on either channel or mode, and after 2-3 seconds of the chord/note sound a very unpleasant low-frequency hum/feedback kicks in. Even if I turn down the FX send pot all the way to minimum (10% mix), it still happens, not as dramatically, but it does. Do you think this is normal? My old Engl E530 preamp was able to handle even much much more aggresive FX settings, without doing this, so I somehow can´t believe the Mesa´s behaviour is OK. And I´m 100% my pedalboard is OK, I have checked it on that Engl - no issues there.... Pls help me on this, I really appreciate all your replies!