2001 Chevrolet Silverado valve tapping

Ok, I've tired all the bandage remedies like removing the valve covers and flushing the valves with b-12, flushing the engine with engine flush to no avail, so how do I fix the problem. On cold start valve are real loud after about 2 -3 second it use to go away, then 2-3 mins, but now it take about 5-10 mins of driving before the tapping go away. So how do I fix it do I have to have the motor rebuilded.