N52 engine metallic engine noise
We took our Z4 2008 30,000 miles to BMW dealer last week (Montreal) and they listened to the knocking noise. It was loud. They changed the lifters. Told us that this would fix the problem. We let them know we had done our research and are aware of the cylinder head fix. They told us we would cross that bridge if we got to it. I guess BMW will be glad when the warranty runs out on all these cars!