Sony Sound Forge record noise

I’ve started to take records from radio via Sony Sound Forge 8.0. The line in input is a very clear signal but while I’m recording, after about 4 min, a low level cracking noise comes up (only when signal)and it is very annoying. I’ve connected a Ground Loop Eliminator in the audio line and if I take it off the described noise disappears but the noise from the net is back of course… I could not identify what it is by now but on Sony Acid pro and other recorders everything works fine. It must have something to do with the program - a setup I believe. I like the Sound Forge recorder and still want to use it but not an alternative!
Who knows help please???