That buzz...
Is the sound of you recording the noise. My theory is, you're using a mic to record the sound playing on your computer, and the mic is part of, or is too close to, your computer. That's what the buzz is. You can use Audacity/Wavepad for the "noise reduction" function to get rid of those buzzes. I won't say the sound is stolen, but I will say if it was a real shotgun, it would be much louder with much more echo. : /