Today my narrowband rx was not working anymore. After a lot of investigation I found that my minitiouner was the culprit.
My nb sdr lnb port is getting 12v from the same power supply as the minitiouner. As soon as I disconnected the minitiouner the reception came back.
I measured the 12v line and noticed that there where some nice spikes and ripples of a couple khz. And this of course switched my narrowband lnb to high band.
The capacitors in the minitiouner seem to be bad and have to be replaced.
Just a heads up.