Originally Posted by: DavesGuitarJourney

I don't think it is a grounding issue. If you look for it there are quite a few posts about this "feature" of the Katana. I knew of the issue and the solution before I bought mine, and was prepared to send it back if the NS didn't completely eliminate the noise. I don't know if this noise is there for every unit or if it is better or worse with different guitars and cables, but it is apparently a fairly common little annoyance. In my experience it was very easy to correct with Tone Studio.

Totally agree Dave. I have a few amps and always turn back to my Katana Mk11 !! I play 90% on the clean channel and love it. However, if I had the choice again, I would had paid the extra few ££££ to go for the 100w, just to have the looper connection.