There've been a lot of complaints about cold-start knock in the Vortec engine family, and most General Motor's customers are getting incomplete answers at dealerships. We've spoken with Matt Kester, assistant manager with GM Powertrain Product Communications, about the situation. He said General Motor's engineers are aware of the problem and are currently in a research stage. The cold-start knock involves the 4.8L, 5.3L, and 6.0L V-8s in all applicable GM cars and trucks from '99 to '02. They believe the cause is carbon buildup on the circumference of the piston above the top piston ring. This interference is affecting the dynamics of piston travel and therefore causing a knock. It seems the problem begins after the first 12,000 to 15,000 miles, and the knock will last between five and 30 seconds in temperatures below 50* after a cold startup. The noise also seems more pronounced after long trips and at lower temperatures. The use of a top engine cleaner will give only temporary results, if any, and a replacement engine without modifications would most likely develop similar symptoms. We were also told that a Technical Service Bulletin is in the process of publication, which should provide an explanation of the condition but not a fix, and that carbon deposits and associated knock are not causing any structural damage to the engine. So, for now, don't let it bother you. We'll give you further details when the TSB becomes available.