I'm not a laptop user but I've read that complaint a number of times. My strong impression is that it is almost always poorly filtered power supply noise - the basic stuff the laptop lives on. I've also seen, without paying any great attention, lists of which laptops work for recording and which don't (don't in the sense of being able to make decent recordings). since the power supplies are not readily replaced with another having better characteristics, you are probably left with battery use. Different soundcards , cables, or any after-the-fact fix is unlikely to be of any benefit....If the laptop has no digital out then an external soundcard with digital out might help. If you can't use firewire (best), look for USB with its own power supply. Too many USB cards (but not all) will pick up the computer's power supply noise on the audio stream if they are using that power for their own operation.