I'm willing to bet you got all over-eager and assembled the engine too hastily without using plasti-gauge to check clearances or carefully inspecting each part prior to assembly. Haste makes rod-knock my friend.
Also, not using assembly lube is a huge no-no. As previously stated oil will not hang on to parts as well for initial start-up. Make sure you don't get any assembly lube under bearing seats or that will totally F- up your clearances.