I have 1997 chevy Z-71 sometimes on startup the engine makes a knocking sound for about 3 seconds and goes away. I dont know if I have a major problem or not can you help?

I think it is normal for these vehicles. My '97 Tahoe did it also and I'd heard it was normal and not to be worried about. Kind of sucks but I had 150,000 miles on mine and it was fine.

Good luck.

Valves, or lifters could be the problem as the previous solution said, but.....

I have, still have a 1999 Silverado 4x4 LS that has the 4.8L with 196,000 miles (give or take a couple hundred miles).

The same thing was happening with mine, especially when it was cold weather time in northern Wisconsin, and I got used to the noise, until one oil change I decided to try the synthetic oil.
Now there is no knocking at all, the noise went away, and I'm really positive it was the synthetic oil that did it. Synthetic oil clings to metal, unlike normal oils, so there is never a metal to metal cold start.

It takes a couple seconds for th regular oil to curculate after you start the engine, and coat the metal surfaces, synthetic oil is still coating even after you turn the engine off.

I won't guarantee that it'll make your noise go away, but for the small increase in cost (and it always seems like the synthetics are on sale) it could save you money in the long run.

I hope this helps you out, and thanks for letting FixYa.com fix ya.

Terry

Check the valves and lifters.