During startup, my engine sometimes makes a slight knocking noise that is normally in-audible in the cabin, but it pretty loud during idle. When I rev, it sounds fine. When it's coming back down, it makes a really bad noise like something's loose. It only happens for about 3 minutes, and then goes away when I start driving. I'm not sure what it is, but no performance loss during driving, and no problems at all. No Check engine light, no problems with plugs(pulled and checked), not sure what this could be...

 

timing chain tensionner?

 

I haven't checked it, but I mean i'm not having one single problem other than a weird sound every few days. I'm working on my buddies Vr6 that has a tensioner problem, and the timing chain was bad on it. That thing made a horrible noise 24-7. I could maybe see it being a slight problem, and progressively getting worse maybe...

 

i timing chain wasnt loose but it was making an awful noise only at idle.dealer replaced it and now its perfect

 

definately the timing tensioner... mine does it... im waiting for it to get wrose until i can finally show the dealership the sound... everytime i take it there it doesent make the noise

 

yeah mine makes a ticking sound on cold starts, but then it goes away...i heard it could just be your injectors making that sound, or supercharger making noise

 

Yeah three things that cause noise at idle:

1. Injectors - Cobalt has noisey injectors.
2. SC - The more miles you put on the car, the more the coupler wears.
3. Timing chain tensioner - This problem usually happens more on the 06 models

 

yeah mines an 2006...how would i know if it was my timing chain?

 

Here, read this : https://www.cobaltss.net/forums/2-0l-lsj-performance-tech-47/valve-train-noise-123100/