Unplug all other devices except what is absolutely necessary. The computer will regularly poll all devices to check that they are working, gather data, etc. This also interrupts the writing process. I have found that plugging in a USB mouse and moving it around while the disc is being written with a USB CD writer makes the sound "edgier" and gives an unnatural hardness and grain to cymbals.The paper goes on to describe the steps this guy takes to minimize the vibrations that his external burner would normally encounter.
I tip my hat to this fellow and his quest for precision burning. And I take comfort in knowing that there's someone who's more ... concerned ... about this kind of thing than I am.