Cadillac CTS 2005 6 Cylinder 3.8 liter

I just resealed the oil pan and changed the water pump. I filled all of the fluids. When I restarted the car the valves are rapping really loud. It sounds like a diesel. I am thinking the oil is not circulating through the engine. I do not recall disconnecting anything electrical that would limit the pump from circulating the oil. Any ideas of what it could be? Appreciate your help.