Hello. I have just put in a rebuilted M20b25 in my e30. According to seller all sealings, bearings, piston rings have changed. The cylinders have been honed. New rod and main bearings. Alonost every bits in the cylinder head are new. I have photos of it all. the motor started up perfect but at 1500-2500 there is as a loud rattle/knocking noise coming from inside of the engine. Nothing to hear at idle. I have checked to see if it is the rod bearings by pulling the spark plug core each and listen if the sound stops. I have just have an endoscop camera down through the spark plug holes to see if anything are dropped inside the cylinders. But nothing there. Any one who have an idea what it can be??