This is from a lawyer's web site, but it seems to clearly describe the cause of the noise:
"GM officials say carbon and the amount of clearance between the piston and the cylinder wall are the primary causes of the knocking.
"Usually, when the piston moves up and down in the cylinder, a component called the ring land, which is near the top of the piston, does not come in contact with the cylinder wall. But when carbon forms on the ring land over time, the ring land gets wider and begins to hit the wall. When the two come in contact, the driver will hear the knocking noise, said Chris Meagher, assistant chief engineer for GM's small-block V8 engines.
"Spacing is also an issue, because when there's too much room between the piston and the cylinder wall, a greater amount of rocking can occur and can cause more noise, experts say."
http://www.lemonlaw.com/gm-engine-problem.html
As Steve and others recommend, don't worry and don't spend a lot of effort on this. Decarbonizing may help any engine including these, but it won't be permanent, and won't make a difference in the long run.
"GM officials say carbon and the amount of clearance between the piston and the cylinder wall are the primary causes of the knocking.
"Usually, when the piston moves up and down in the cylinder, a component called the ring land, which is near the top of the piston, does not come in contact with the cylinder wall. But when carbon forms on the ring land over time, the ring land gets wider and begins to hit the wall. When the two come in contact, the driver will hear the knocking noise, said Chris Meagher, assistant chief engineer for GM's small-block V8 engines.
"Spacing is also an issue, because when there's too much room between the piston and the cylinder wall, a greater amount of rocking can occur and can cause more noise, experts say."
http://www.lemonlaw.com/gm-engine-problem.html
As Steve and others recommend, don't worry and don't spend a lot of effort on this. Decarbonizing may help any engine including these, but it won't be permanent, and won't make a difference in the long run.
