I'm not getting to the lifters or the tappets, they are more than likely fine. It's a known issue for the o-rings in the sump to fail, and cause a lot of air to get into the system. They all tend to fail around the same time, and usually fail soon after a oil change. My issue started about a hundred miles after an oil change. I changed the oil again then, thinking it was an oil issue, but no dice.
http://www.matthewsvolvosite.com/forums/download/file.php?id=5580&t=1