Hello, I'm using Ampeg SVT-3 Pro and Yamaha FX770 Multi-Effect in it's effect loop. I'm getting some kind of distortion when i turn the volume up to half and more. It continues even if i bypass the FX770. When i unplug it the distortion stops. I check all the level settings on the units but there is nothing seen to cause this kind of distortion. What can i do to stop it? If i change the FX770 with another effects unit like TC. M-One XL, Boss VF-1 or Midiverb 4 can i have the same problem again?