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

@Native68

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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?
 

@Native68

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I have the same issues. Have you resolved the knock issue?
I have not. I keep asking around but no one has an answer. I'm going to keep trying. If I get an answer, I'll update the post. Please do the same!
 
G

G-660807

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?
I have the exact same thing. The truck was quiet and super smooth when I bought it. I think it shifts down easy when it rattles also.
 
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G-576178

I have exactly the same issue with the same truck (2020 AT4). Looking for a common theme, have either of you used a diesel additive over the winter? I live in Ohio, and we've had a few near-zero days, so I've used Power Service Diesel Fuel Supplement + Cetane Boost to keep the diesel from gelling.
 

@Native68

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I have the exact same thing. The truck was quiet and super smooth when I bought it. I think it shifts down easy when it rattles also.
I notice the noise more in city driving than highway driving. I have found if I drive in sport mode, the shift points are at a higher RPM which keeps the knocking to a minimum. Still concerning.
 

@Native68

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I have exactly the same issue with the same truck (2020 AT4). Looking for a common theme, have either of you used a diesel additive over the winter? I live in Ohio, and we've had a few near-zero days, so I've used Power Service Diesel Fuel Supplement + Cetane Boost to keep the diesel from gelling.
Negative. No fuel additives. I only fill up with the GMC recommended Top Tier fuel. It's does contain a percentage of biodiesel, but doubt that is the issue. Have you had any luck with the supplements? Although I'd like not to do it, I have contemplated adding a FASS fuel system hoping to remove all air from the fuel line. Duramax Diesel Performance Parts
 

ElevationMax

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Following as well picked mine up Tuesday 550 miles in hearing this same type of noise... Have had many diesels and sounds like the engine has spark knock like a gas motor nice and quiet at highway speeds. Just taking off at low speed when this happens.
 

@Native68

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Following as well picked mine up Tuesday 550 miles in hearing this same type of noise... Have had many diesels and sounds like the engine has spark knock like a gas motor nice and quiet at highway speeds. Just taking off at low speed when this happens.
Yep, that’s it. Weird sound. I hope we find a solution.
 

GMCAT4

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same issue between 1500 and 2300 rpm on new 2021 GMC Sierra AT4 3.0 liter diesel with just over 500 miles. I also started using Sport Mode or Trailer mode which reduces the clatter due to higher rpm shift points.
 
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Satinsteel

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Could this be a centane issue? Centane being the diesel equivalent to octane in gas.
 
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G-404239

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?
Same here
 

Wheels619

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I'm also having the same issue with my silverado 3.0 duramax. It's at the dealership now but they cant seem to recreate the noise. Which to me sounds like a load. They are having it driven again in the morning to give it a listen.
 
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