Not the usual diesel knocking - 3.0L Duramax LM2 Diesel I-6

I am having the same issue. Sometimes the exhaust smells different to me when its idling. Last night I was at a traffic light stopped and I felt a bang and then again. I watched my tach and noticed with the bang my tach dropped almost like it was missing. It didnt throw any codes but I am very concerned for a $73,000 truck to be sounding like this with 18,000 miles on it. I will keep following this thread.
 
Glenn Davis said:
I am having the same issue. Sometimes the exhaust smells different to me when its idling. Last night I was at a traffic light stopped and I felt a bang and then again. I watched my tach and noticed with the bang my tach dropped almost like it was missing. It didnt throw any codes but I am very concerned for a $73,000 truck to be sounding like this with 18,000 miles on it. I will keep following this thread.
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Mine is going in tomorrow, I worked for GM for 10 years.. my diesel tech is telling me it’s common for these to have lifted issues and timing belt issues that can cause this noise
 
2021 GMC Sierra Elevation 3.0, 9,200 miles and coming up on 1 year with it.

Started hearing that same knocking sound beyond the normal diesel earlier this year, which is definitely worse in city driving. I haven't taken it in for the noise yet, but plan on bringing it up at the next oil change.

I'm not very hopeful just based on my experience at the last appt where I mentioned a whistling/howling sound from driver side door/window on the highway in a cross wind. Even after I showed the techs videos of it, they pretty much said they would take it out but if they couldn't replicate the issue then there was nothing that could be done. They noted it and told me to try to keep recording it when it happens to potentially escalate it to GM. I think it just needs a new door seal, but trying to get that is harder than getting wisdom teeth pulled.

So, part of my $52k GMC experience is learning to enjoy the deafening howling pitch like someone is screaming into my ear (good news is at least it only happens occasionally!). When it does happen it scares the s*** out of me, last time I was caught off guard so much that natural reflex caused me to swerve into the shoulder. Has anyone else dealt with this type of noise? Tech said he thought it was the mirror....

The other question I wanted to ask is if anyone else has experienced their engine getting much louder? I understand a diesel is louder than gas and engines get broken in, but my truck has gotten WAY louder from when I bought it. It's louder than the 6.6 in the HD's. Hopefully it doesn't get to that old school Cummins level.

I've been a GM person since I could drive, had 2 Silverados and a Tahoe before this Sierra. They were all good vehicles. I really do like the truck, but been thinking with the current market about selling or trading it in.
 
Hi guys, has anybody investigated the cost of replacing the oil pump belt required at 150k miles? I know it will take a while until we see engines with that kind of mileage. I'm planning to get a 2022 Elevation by mid next year. I went to drive test at the dealer, and they told me that at the dealer the job would be around $6k!!!!! What would be an alternative to do this job at a lower cost considering I don't have the capabilities todo it myself at home?
 
I'm in the same boat. I have a 2021 GMC At4 and have just starting hearing the knocking noise. This only happens at low rpm just as the other descriptions above. Has onyone found the culprit or do we just live with It?
 
If it's knocking under light acceleration it's a fuel knock because the timing is being advanced. It goes away when you gradually depress your accelerator to increase the load.
Normal.
 
I've worked on heavy duty Cummins in the past. Mechanical and electronic. I found when the engine is under a light load you could hear that knock and would go away when you stomped on it. The ignition timing advances under light load and retards under load. This has been a thing since the OLD mechanical variable timing and now with electronic diesels.
Nothing to worry about. It's less noticeable when the engine reaches operating temperature.
 
@Native68 said:
I have a 2020 Sierra AT4 with the 3.0L Duramax; 5th truck, first diesel. I love this truck, especially the torque at low RPM's. I've put about 7,000 miles on it. I am not a hot rodder. I am a 1,500-2,500 RPM driver. At lower RPM (1,500-2,000) the engine sounds more "knocky" than what I wouldn't expect from a diesel. It sounds similar to the knocking of gas engine with low octane fuel. I've checked all electronic diagnostics and the all stats are good (green checks). The only way to eliminate knocking noise is to drive in Sport Mode (higher shift points) or at a higher RPM. Any comments or suggestions?
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have you tried and diesel additives to clean the jets?
 
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