Kind of had this problem last week, but don't know if its the same noise. What was happening was that the cam was walking forward and the chain was creaking because it was out of alignment. It was almost as if the cam was screwing out. I thought maybe because I replaced the #3 cam bearing (scored from oil feed hold directly toward the edge of the bearing. At any rate I looked from the side and saw a pretty good gap between the cam gear and the thrust surface. Took off the rockers and tapped the cam back and noise went away.
Just a thought