i have just rebuilt my ls block with new rod and main bearings and rings. when i start up the car from sitting overnight it knocks and rattles for aobut 2seconds and the oil pressure light is on for those two seconds as well. i am running 5 w 30 oil right now because it only has 200 miles on it. is it normal for a new rebuild engine to make these noises for a little while till every thing breaks in and i switch to 10w30 oil?

 

it isn't normal for it to make knocking sounds especially if the oil pressure warning light stays on for a few seconds.

What oil pump are you using?