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Originally Posted by sTUNNA
When you say the "clicking" sound, do you refer to the noises the engine makes after the car has been turned off, cause mine does that for maybe 5-10 minutes after I turn off the car. Or maybe Ive never realized it while driving. Mine makes a popping sound every 3 seconds.
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that noise is the exhaust and catalytic convertor cooling down. metal cracks when it's expanding and contracting. completely normal, nothing can be done.
as for the "cold knock", i'm a GM technician, and i've seen this a hundred times, along with my own yukon. when gm designed the engine, they made the piston skirts shorter to save weight on the pistons. this made the pistons "cock sideways" in the cylinder and make the slap noise that you hear. actually, they only move about 2/1000ths of an inch, but enough to make noise. it does not hurt the pistons or cylinder wall at all. mine has been doing it since 25k miles and i'm now at 135k. not worse or anything.
the top engine cleaner does work temporarily, but only if it's dumped directly into the cylinder. not drawn through a vacuum port. the noise will come back.
hope this helps.