Hello, after a significant amount of troubleshooting and correspondence with Kemper, their recommendation was to return the unit for exchange. Unfortunately it was not a user serviceable issue. I was disappointed that a factory refurb unit had the problem, but was very happy to get a NIB unit as an exchange.
The problem in mine was intermittent as well, it would usually show up as much as 1/2 hour after first use. Sometimes it would start immediately.
Sorry to hear you might be having the same problem.
Hey did you ever find a solution for your distortion in the alternate input? I have the same problem and no matter what I try cant fix it. I change some cables today and it went away for about 20 mins and now its back to haunt me once more.