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.