Although this thing is sick and all the reason only 1 was built was because its hard to set the timing right, there's to much liability for Cadillac. They would've had way too many recalls otherwise they would've gone with it
Could be due to using regular gas. I had that same exact problem with mine and started only putting premium in it. That engine knock has now disappeared. Then once I put regular In and the knock came back. So now I only use premium in mine.