Do you have a flopping piston on a wrist pin in that engine? Like maybe a wrist pin fractured possibly. I had an engine sound just like that and it was worse when the compression wasn't putting pressure on the piston and it allowed it to literally flop around in the cylinder from the worn out pin.
If your going turbo, your going to put a major stress on engine parts. If you don't go through the engine and replace/rebuild things, you may find out rather quickly which parts were the weakest, lol.

Great build also...keep it going.