I have found a solution to the problem!
Thanks for helping me out guys!
I opened windows mixer and muted "mic in" though it was muted on the "out side".
Then the sound became perfect. However the radio volume worked, when i adjusted the "recording" slider.
The "line-in" slider in windows mixer was greyed out, so I could not adjust it.
(This also may explain that I could not adjust volume in CF.) It stands at about 70%.
This means that the "recording" slider has to be at the very bottom to get a decent volume. Any way to make the "line-in" slider work?
I'm using Infill G4 with onboard sound card, no usb card. Newest Xp drivers.