Im getting a knocking noise after warm up and then goes away again

What is your question?

I have a 98 5.7 silverado with 210,000 miles on it. I've been using a high mileage 10w-44 I think it is with a k&n oil filter and a bottle of lucas. Im getting a strange knocking noise. It only happens after a couple mins at start up. Im in 100 degree weather right now too. So I start it, give it a min to warm up and then by the time I get down the street to the stop sign I can hear the knocking / tapping sound. After like eight mins of driving the noise goes away. What oil would you recommend I switch to? And should I try a different brand? Im running a high mileage synthetic blend.

How long has your 2000 Chevrolet Silverado 1500 had this problem?

Couple months