If he indeed means "crackling" like a fire, and not just general distortion, I'm not sure what it could be. The "Mountain of Dreams" song he linked to, however, does sound like a lower quality sound font, or something similar. Maybe a lower bit rate was used on the sound font (as opposed to the mp3 itself.) If I turn it way up I do hear some distortion which could be misconstrued as "crackling", I guess..
To me it's a lower quality piano sample that's being used.. IMO..