Hey, I just came back from my first gig with my recently bought (one week ago) Kemper Power Rack.
I had a Twin an AC 30 and a Bogner ecstasy with me. Used my Mesa 1x12 as monitor.
The short story would be like: I had lots of fun. Not much to carry. Everything put in place quickly. Decided to skip my in ears since the drums have not been too loud.
Then all of a sudden (during sound check / final rehersals of some songs) I heard a strange sound. And then it was gone. After a while (the noise got "static") I checked everything. It sounded like the master signal from the PA. But how could that happen? I changed cables and checked my backup guitar. Nothing. I set up my tube amp. The same. How could that be? I checked the setup at home with no problems so everything sould be perfect.
The answer was quite simple. There has been an installation for people with hearing devices which caused the problems. The master signal got picked up by my guitar...
After switching that system off everything was perfect.