I'm pretty much an ignoramus on audio technicalities but have a similar problem to the person with "hiss" but that thread hasn't solved this problem for me. I have a "broken" humming background noise on voice recordings I am making for commentary on a video. It sounds a bit like mains hum but is interrupted. I have uploaded a sample at click here
I am using a headset mike plugged into a Dell Insopiron 6000 laptop.