Knocking sound

[Gorgis2]

I have a 2021 GMC Sierra 1500 Denali Duramax 3.0 diesel with 13000 miles. I have been experiencing a knocking noise when I reach 20 mph and it continues to 40 mph. The dealership says they don’t hear a problem. Does anybody else experience this? Is there a fuel additive or oil additive that i should be using that may help? I’m new to diesels so suggestions would be appreciated.

[silveradosid]

engine cold or warmed up, what was the outside temp 

[Gorgis2]

18 minutes ago, silveradosid said:

engine cold or warmed up, what was the outside temp 

The sound begins after driving for about 4 miles when the engine temperature registers about 200 degrees.The outside temperature have been in the teens and 20s. 

[Transient]

Are you sure it's the engine and not something else?

[Gorgis2]

4 hours ago, silveradosid said:

engine cold or warmed up, what was the outside temp 

The sound begins after driving for about 4 miles when the engine temperature registers about 200 degrees.The outside temperature have been in the teens and 20s. 

[Gorgis2]

As far as I can tell it is coming from the engine. As I accelerate the knocking sound gets faster. It reminds me of a sound I had in an older car years ago when I used a lower octane fuel.

[silveradosid]

did you notice this after filling the tank

[Gorgis2]

On 2/5/2022 at 7:58 AM, silveradosid said:

engine cold or warmed up, what was the outside temp 

The sound begins after driving for about 4 miles when the engine temperature registers about 200 degrees.The outside temperature have been in the teens and 20s. 

[Gorgis2]

I notice the sound after a week after filling up the tank. The gauge registered half full.

[customboss]

SCR system valving freezing or sticky cycling? 
Functioning so there’s no threshold of throwing MIL code?