2001 k1500 5.3 with 104,000 miles. Started several months ago when engine was started but would get quiet after 10 or 20 seconds. Now it knocks longer and louder but does eventually get quiet. Sounds louder than a lifter. I'm wondering if a piston. I bought the truck about 4 or 5 years when it had 56 thousand on it. Truck looked new when I bought it and did not notice and problems with engine. Since then it has gotten fresh oil every 3000-4000 thousand. Most of my miles are highway. And from the look of the truck I'd guess most of the previous owners mileage where highway. I'm bummed!!