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I have a 2002 GMC Envoy. Last year it developed a knocking that was at a very low volume but became louder in a 2 week span. After that it's been the same, it's louder when the engine starts cold and then becomes quieter when getting hotter; still it's somewhat loud. I've kept driving the car daily since then without any trouble. I guess it's not rod knock, any clues?

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Another thing it could be is a failing exhaust gasket between the header and the head. These types of leaks will exhibit the knocking sound, but often quiet when things warm up and expand. Sometimes they'll only make noise until things are warmed up.

While not fool proof method, one way to detect this type of leak is to look for black soot emanating from around where the header attaches to the exhaust port at the head. It can be hard to see, especially on the bottom side of the header. If you see the soot traces, you'll know you should at least get this fixed before you proceed further.

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any way to record and upload the sound it is making?

Usually a knock does not happen when the engine is cold and at low / idle RPM. Have you kept up with changing your oil and did it run low last year? Did you see metal particulate clinging to the drain plug or dipstick? Is your oil pressure low or is it missing an oil gauge?

If the noise lessens when it gets warmer that usually means something has expanded and is now fitting better than it was before. how long till it's quieter and how much quieter is it?

My first guess is you may have the beginnings of rod knock but not sure here is a video of how to find out and what it is. If it is nearly still fine then it may be hard to feel the looseness as shown in the video going through the spark plug hole.

It could be a failing hydraulic lifter to.

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