I (finally) just got my Kemper non-powered head last Thursday, didn't get to work with it 'til Friday (updated to latest FW first off), and have been experiencing this same phenomenon. I've been testing several setups and it's revealed itself in headphones and studio monitors, however, I don't recall hearing it when MONITOR OUT to combo FX RETURN.
I cannot make this happen as it is intermittent between changing rigs via the Kemper and Rig Manager/Exchange software. I've not connected a MIDI controller, yet. It does not always happen on any particular rig or order and (again) I cannot repeat the same load process to recreate the effect. It is intermittent.
Just popped on the forum and searched "fizz," resulting in this post.
Any developments and/or recommendations?