I have read this thread pretty carefully and would like to thank everyone who contributed. Here's my contribution!
There is a new service bulletin that specifies to replace the exhaust side lifters with the new design, and to replace the cam followers (rockers) with new ones as well. Apparently this is the first time my dealer has done this new SB with the rockers included. I asked for a copy of the SB and the foreman smiled and shook his head. He knew I had read up on this extensively online, and I don't think he wanted me to leak it to the interwebz.
This came about after I left the car with them. I heard the noise on start up last week. They replicated it yesterday and are replacing all the lifters and rockers under warranty. This is a 04/08 production E91 328xi.
edit: this diagram helped me visualize the components. I was very familiar with an E30 head; this bridged the gap.