run on battery
there's nothing you can do about a laptop power supply generating noise/buzz--that's one of the problems of using a laptop to record. make sure you've got all of your gear plugged into the same circuit (helps cut down on ground loop buzzes).
when i have to use my laptop to record, i pull the plug and run on battery while i'm actually recording. then during "down times" i plug back in and grab a few minutes of juice.
so, get a bigger battery (or a second one if your system can handle 2) and use that. otherwise, you're gonna have to learn to live with the buzz.
not to mention, you can't really edit out the buzz (through NR plugins, etc), as it's so prominent and usually varies in frequency, oscillation and volume. the only thing to do is avoid it in the first place.
me thinks you'll be looking to move to a desktop soon enough....
wade