my engine sounds like it knocks for about a second or so after i start it. its kinda loud and didnt know if anyone had this problem

 

Its called "piston slap" and is concidered normal by GM. Sounds like a knocking or ticking sound only right at start up on a cold engine. Almost all GM cars and trucks do this now, have been for the last few years. Take it to your dealer for service, if its excessive there could be other problems.

 

that sucks. It's almost embarassing. Oh well.

 

MAke sure it's definitely the case. I had the same thing. Though mine sounded like a valve tap in the morning right after i'd start it. After 2 trips to the dealer, where I left overnight so they could here it on a cold start, they told me that it was within "acceptable" limits.

This is a leased 08 btw. So after being sick of hearing this I made another appt and when I got down there I told the service guy I've had cars with over 250k on the engine that did NOT do this and it was completely unacceptable. This time though the service guy was a different person as the dealer had changed hands. So after keeping it over night, they called me the next afternoon and told me that it was actually the exhaust manifold leaking. And more specifically, when they went to remove the manifold they found the last bolt closest to the cabin, was sheered off. So they worked for 6 hours and could not get the sheared off portion of the bolt out of the head. So they ordered a new head, and then on the last try, they technician got it out.

Anyways, just have them make sure. If your dealer is anything like mine lately, they've been doing anything and everything to make me happy. Free Hummer rental for replacement, etc... They said they need to make sure they get all 'A's on those surveys that GM sends to you after your service appt.

 

These motors also have what is called cold start strategy. The PCM will change the VVT (variable valve timing) upon cold starts and you will hear valve noise for a split second while this is being adjusted.

 

Hey Kid Stuff, I am with JRBNC on this one. I just got out of the dealer. With the same problem, except I had TWO busted bolts and fortunately, they were able to tap them out and replace the studs and the gasket.

I noticed a bit of a ticking on start - and it NEVER DID THIS BEFORE. That was followed by what sounded to be like an exhaust leak when the engine was under a heavy load. I think that this inadequate back pressure in the leaking cylinder(s) was causing a valve or two to float and knock so I finally took it in and they did all the work under warranty with a rental.

Now the engine honestly feels like it has a bit more power and it never starts with a knock no matter how cold.

Good Luck!

 

If it only happens when you first start a cold engine that has been sitting overnight, it could be this:

The engine has hydraulically actuated timing chain tensioner that requires the oil pressure to first come up to add the required tension to the timing chain. Over time the chain will stretch so the tensioner has ratches that will click over to the next position to correct for the slack in the chain. Similar to how self adjusting brakes worked.

When you first start the cold engine, if the chain is loose and before the oil pressure can come up to take up the slack, the chain will slap the insides of the housing. It sounds like a rattle that immediately goes away.

What is happening is the chain is loose enough to slap but not yet loose enough for the tensioner to click over to the next position. Do not listen to the dealer when they say something stupid like "they all do that." They don't. This is a design error.

GM has very lose tolerances on their parts. If both parts are on their outer tolerance limits, the combined effect is what happens. This is a warranty repair.

How do I know? Fortunately there is a Lemon Law in Florida and only after exercising my rights under the law did the Facory Rep correctly diagnose the problem.

But then on the other hand, you may just have an engine knock.

 

Mine is in the shop right now getting the EXACT same thing described above worked on. Right down to the sheered bolts and the sound that I originally thought was valve tapping too.

Dealer gave me the same BS about that's how the engine sounds, but I knew something wasn't right. It took me 4 visits to get those AHoles to admit the problem.

This has got to be a factory issue.

This will be my last GM vehicle. My next offroader is probably going to be a customized Titan...

Also, I wonder if you guys are having some of the other problems I have had. I am on my THIRD SET of TAIL LIGHTS. The cheap plastic keeps spliting.

 

Well so far I got a exhaust rattle, both roof rails are broke, engine sounds knocky at startup, bottom of the rear passenger door is rusting. But I love it still.

 

I had a broken radiator mount weld that was causing a clank when going over bumps on the front passenger side. Thought it was related to suspension, but they finally figured out thats what it was. Also had a leaking rear diff cover and some loose suspension parts making the handling bit off. My front abs sensor wire busted while on the trail the other day, but it was while going through muddy water, so I can see how anything got up there to break it. It basically looked like someone just cut it in the middle. there was a bit of flex with the suspension going over some rocks and odd angles. it seemed to me that wire has no play at all if you maxed out the suspension maybe that put pressure on it. but who knows. In any case the service guy is real cool and said don't worry about it and it was covered under warranty. 1 hour next day and fixed.