The buzzing sound is most likely a ground loop.
There are a number of ways to address this, but the safest would be to head to the local Radio Shack and pick up a Ground Loop Isolator which looks like a pair of RCA cables with canisters in the middle of each lead. Cost is about $20.
Another would be to use an ebTech HumX on your laptop. While a little more expensive, it’s a GREAT tool to have in your bag.
