I've shot an H&K23 with subsonic rounds and an AAC supressor on it, it's pretty damn quiet. I did get a chance to shoot the volquartsen Mark III Ruger, and enjoyed it.
But for a belt-fed machine gun for on ground support, that is capable to be handled by one man, it is impressive. There are a few times in Iraq we could've employed something like that, instead of our M249 SAW's.