Engine Catter at startup on 1990 Chevrolet Suburban 2500

The engine clatters upon startup, and quite's down upon idle, then knocks slowly after warm up, but runs smooth and strong no engin missing at any speed. Any Idea's?

sounds like your lifters are noisy maybe try a different brand of oil and add some lucas oil treatment to thicken the viscosity of the engine oil,
Thanks Hemicuda, I gave it a try it muffled it a bit, but it is still there, I narrowed it down to the #4 piston area, but cant be sure if it is a lifter or what, when I unplug the sparkplug it stops the knock. Idea's?
yep ... can definately help you on this one ... trade it in or sell it cause you have a bad wrist pin ... it connects the connecting rod to the piston and its pretty expensive to fix ... also chances are its not the only one ready to go bad ... if you do plan on keeping the vehicle your best bet is to install a new crate engine or if you want to fix it yourself the buy a new short block assembly ...
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Just about every factory GM motor after the mid 80s came equipped with hyperreutectic pistons, these pistons are an aluminum alloy with a high silicon make up, the piston do not reach true size in the cylinder until they build up some heat and come up to operating temperature, as a result the make a noise very similar to a rod knock, the noise is actually a cold undersize piston slapping against the cylinder wall, ive read in many articles that this short perion of slapping will not harm the piston or the rest of the motor for that matter
Just a update, I rebuilt the Engine in January of 2010, found bad pistons and mains put a new roller cam in and updated every thing else, got it running and sold it, I had to many issues with that truck,Now I'm working on a 95 Dodge 4x4 It needs a new Transmission, I'm currently pulling it out should be drivable by May. Thanks for all the Help guys, And looking forward to your help in the future. Tractornuts,,,