I'm still looking for a way to record directly from radio/amp onto the computer, be it via the internal or an external (Creative Soundblaster) soundcard, but regardless of how I connect things (my notebook and the radio or my notebook and radio-via-amp), I get a low hum that is very annoying and is present on the recording as well. 
I did plug in the radio in all rooms of our apartment, including bathroom and kitchen, and it won't change... 
My computer is a notebook (though I'll have another one soon too, hopefully, but I still need a monitor and a friend to help me setting it up anew), in case that matters. 
 
Anyone has an idea what can be done about that? Looking for a new place to stay with more than just two fuses? (not an option, of course!) 
And could the feedback problem not be present if I was using the desktop computer?