No, nothing particular, but in fact, as far as I remember radio traffic was lower when everything was disconnected. But the radio traffic is not the real issue here. The problem is the non-deterministic quite loud noise, which comes from Dunnowhere.

Well I made some measurements with a spectrum analiser on that sound. And I found that it is like a white noise on the frequ band of the guitar sound.
There's no triggering action. It simply comes, and goes.

The next thing I'll try is to take it somewhere else (out of the house - I tried in the living room - the same stochastic noise came). Ah, one more to the line-out. There's an output on the multieffect, which was designed for headphones. I used that one, so that should not present a problem.