This happened last august. I had just got the car back after being away for 6 months getting a cage, custom cams, return style fuel system and a methanol injection kit. I'm just now getting the engine back together after finding out what the damage was.
This is what it sounded like after the 13th pass. The meth injection line blew a hole and cause it to go lean. This was a built engine. It made 656rwhp through a C4 transmission.
http://i160.photobucket.com/albums/t165/y2k2gt/th_100_2504.jpg
After replacing the rod bearings with the engine still in the car and the lash adjusters it made the same noise. I pulled the engine to figure out what happened.
http://i160.photobucket.com/albums/t165/y2k2gt/100_2984.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_2987.jpg
The marks on the pistons are from a borescope I used.
http://i160.photobucket.com/albums/t165/y2k2gt/100_2989.jpg
This is where the noise was coming from.
http://i160.photobucket.com/albums/t165/y2k2gt/100_2994.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_2997.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_2998.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_3003.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_3150.jpg
http://i160.photobucket.com/albums/t165/y2k2gt/100_3149.jpg