If this is as a result of the power supply being plugged in (which I'd bet my right hand on) there are a few ways round this:

a) get a ground loop isolator - http://www.maplin.co.uk/Module.aspx?...amp;doy=search

b) remove the top pin from your power supply, if you don't want to mess around with your power supply buy a three point block splitter and remove the top pin from that - this of course is slightly dangerous, but you're unlikely to get a serious shock from a laptop

c) plug your laptop power supply into a different elkectrical loop if you are lucky enought to have one close to hand - In my living room one wall is on a different loop to the other, so long as I plug my laptop into the socket on the other side of the room to my decks/amp etc i get no noise issues :D was well chuffed when i found this out.