Every morning my Dad's truck (20002 Chevy 2500HD 4x4 Vortec 6.0L) does this weird thing when it's cold in the morning, like it idles really low, then revs up to 2,000 rpm, then low idle like it wants to die. It will die if you don't keep your foot on it. And sometimes it even backfires out the intake! I think tomorrow I will take the air filter out and start it to see if it's not getting enough air. Overall, a GREAT truck!!!
I have a 2004 Silverado, and tow with no engine problems. I now use synthetic Mobil 1, and am using Napa Gold filters. I put a K&N air filter on mine. I never use cheapo oil or filters. I also never run my cars with 1/4 tank or less of fuel to prevent fuel pump wear.
I think some people think they are just trucks, and do not change fluids and filters as they should. This goes with imports as well.
I have an 01 with an 8.1 as well. It's always made those sounds on start up. It's never affected anything, and now I'm rounding the 300k mark with the factory injectors, and just put in my 3rd set of plugs and wires too. I think I'm going to drive it till it finally just won't go any more...
Your problem is common. It's usually a little carbon build up and won't hurt anything. It's annoying but common.
I found that using a tank of premium or Lucas fuel system cleaner knocks the racket down some. If it's really loud and continues to get noisier while driving, do a compression test on it. Or make them do it at Chevy.
Also... you may be hearing some of the injector rattle as well... All pretty normal, and you should be fine.
I have well over 275k on my 8.1, and it's done the same thing since day one... I've never changed anything but plugs and wires.
Good luck with it.
Mine had carbon buildup in the cylinders. I used Lucas carbon treatment in the fuel. It sounded great after two tanks with Lucas twice.
Sounds like you have a worn piston connecting rod bearing. Change the oil and filter, and put in 20/50w oil and Lucas oil stabilizer. Should get you longer engine life, and will quiet your knock.
It's not gonna blow up from the knocking problem. The 2001 & 2002 6.0's made noise from piston skirt slap. I have a 2002 1500HD with over 180,000 miles on it. Yes, it makes more noise on cold mornings than warm ones. When it was new and under warranty, I tried to kill it then (hit the speed limiter a number of times) and she still didn't blow.