I have a 2001 2500 hd with a 6.0 liter engine. Ever since it got over 80 thousand miles on it it had a knock when it was cold. The truck has about 104000 miles on it now and it has gotten louder. Sometimes you can barely hear the knock and sometimes its really loud and even after it gets warmed up you can still hear it. I was just wondering if anyone knows what the hell causes this and if there is anything that can be done besides rebuilding the engine to fix it?