Sorry for the delay in getting back to you Tony. I shoot pyro too and am naturally very busy during the Fourth of July! Your amp is a solid performer so I can't see any problems with that. I've never used that particular mixer but doubt that's causing any problems either. At this point I'm not sure what to tell you. Are you using any wireless mics? All I can really suggest is to take your system out at home when you have some time and go piece by piece swapping things in and out until you find the winning combination that fixes (or at least isolates) the problem. I've never had a problem like this myself that I wasn't able to explain, and I would think that if this was the case with these particular units more people would be complaining. That makes me think it has to be something local in your system, but beyond that I'm out of suggestions! Best of luck trying to fix this!