I have the Kemper Powered Rack and use it with my Mesa 4x12 cab. I also have a Eden 2x12 I use at home for rehearsal. My problem here is that most of the stock profiles on the Kemper have a ton of horn noise. I thought maybe buying some professional profiles would fix this, but sadly no luck. I've also profiled a few amps and preamps of my own and still getting this horn noise to some extent.
It can't be the cabs because I've also tried it with other cabs and the signal comes thru the main output. I also don't think that all of my basses active and passive would be the problem.
Is there maybe something I'm doing wrong?