Michael Dean says that the most common source of background noise in audio podcasts and the music you record at home is the sound of computer fan that is captured by a sensitive microphone because you are recording close to the laptop computer.
Dean there suggests using a microphone away from the computer or buying an additional desktop and use it only for recording digital audio – no Internet, no gaming.
“The basic solution for this is to get your microphone at least six feet away from the computer. Use a directional mic and point the sweet spot (the side of the microphone that picks up the most sound, usually indicated by a dot on the mic body) away from the computer. With a USB mic, you can often use a USB extension cord.” Link.