New here with my new 07...problem?

[NJ Denali]

Hey all, I just picked up my 07 Denali because I need to tow a bit. It has 19k miles and is an immaculate one owner purchasd from a dealer.
I noticed what sounds like a knock that occurs when cold. You can only hear it under load, not in park. On one hand it sounds like a rod knock, but because it's only under load I'm thinking possibly a cracked exhaust manifold?
What doesn't make sense is that there are no signs of any other problems. No smoke, no CEL's or anything.

Any ideas would be appreciated.

Thanks in advance...

Jeff

 

[NJ Denali]

OK to add further, it's a 6.2 6 spd. On the one hand the noise concerns me, but since there is no other signs of anything at all I'm not sure what to think. I'm not sure that bringing it back to the dealer I bought it from will help. I already brought it to their attention and they chalked it up as nothing. Maybe it is, but I'm not sure what to do from here.
I'm an avid car guy, but this one has got me stumped. I can't check it myself because it only is obvious while under load.

 

[InTruckDesign]

Sounds like you are hearing detonation ie: pinging, especially if it happens only under load. What octane fuel do you use? Next tank should be 91+ and dump a bottle of fuel system cleaner in the tank.

 

[NJ Denali]

I wish that was the case, but it's not a detonation sound I'm hearing. A cracked manifold or exhaust component can exhibit a similar sound under load. The engine "twists" in drive and can open up a crack where it might not in neutral. Quite honestly, that is my only hope other than a rod knock that quiets up as the engine warms. It's almost loud enough to sound like a diesel for the first 5 miles and then goes away.
I don't get it...everything else on the truck is perfect.

 

[Conor]

Sounds like a trip to the dealer for a warrenty claim with only 19K on it

 

[taho26]

Sounds like a trip to the dealer for a warrenty claim with only 19K on it

um yea...id drop it off and say dont give it back till sound is gone or its been confirmed normal

 

[InTruckDesign]

how long do you let it warm up before driving? or is it present regardless of engine temp.?

 

[NJ Denali]

how long do you let it warm up before driving? or is it present regardless of engine temp.?

I let her run for 30-45 seconds before driving (longer in colder temps). The noise stays present through 185 degrees and starts to quiet at 210. Running time is between 5 and 10 minutes and then it all completely disapears. There are no signs of the noise in park or neutral (only under load). There are no signs of any other issues whatsoever. The exhaust seems loud but in a good way; I thought maybe there was a crack in the exhaust manifold that was more evident when cold, but there are no signs of exaust fumes?

---------- Post added at 08:37 PM ---------- Previous post was at 08:32 PM ----------

I have to drive to the dealer early tomorrow and let it cool down to cold so I can show them the sound. I'm hoping they'll do the right thing. If not, I purchased a GM warranty and will bring it to my local Chevy dealer.

 

[InTruckDesign]

I know that the previous generation 5.3/6.0 had cold start knock, but that happened in all gears. Being that it only happens under load, or in gear I wonder if its driveline related and the sound is just being radiated towards the motor.

 

[NJ Denali]

Brought it to the dealer this morning and had the same thought. I watched the trans temp to see where the noise stopped and it was at about 100 degrees. I sat at the dealer for two hours for it to cool down enough to show the tech. We took a short ride and he heard it right away. He thought it was the cold knock too, but called GM just to confirm. They are having him tear it down to the lifters. Apparently GM had a problem with Eaton lifters on the 07 6.2 litre. They changed lifters in the model year, but if it is the Eaton's they will replace them. We'll see what happens from here.