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I just bought a 2020 Gmc 2500 Denali with the 6.6 duramax I’ve put about 3000 miles on it and noticed a knock noise it sounds just like a main bearing knocking so I brought in to let the dealership look at it and there telling me that the knocking sound is coming from the return oil pump and that is normal. Has anyone experienced this noise ?
I was thinking about bringing it to another dealer and see what they say but don’t want to look like jackass if any can help me out with this please let me know
Thanks everyone and thanks for letting me in yalls group
Eric Z
 

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I posted a similar problem last week with my 2020 and posted it under "thumping sound". Dealer told me it was from the "egr system" and of course it is normal. Obviously they just blow you off because they either don't know the answer or don't want to take the time to troubleshoot. My sounds basically the same either a knock or thumping sound which is loud enough to hear from inside the cab with the windows shut. It increases with the rpms and is more noticeable at idle. On fast idle when cold you really can't hear it but as soon as the engine warms you can hear it. This is my 4th dmax and none of the others had this loud of a noise. Trying find another 2020 to compare with mine. Most likely need to try another dealer of look up a good diesel repair shop that knows the dmaxes and let them check it out. If I ever get an answer I will post it. Good luck, jhc
 

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I have the same problem of knocking, it started after changing the oil(Amsoil 15-40w Diesel) at 1300 miles on it. When cold the engine runs quiet, when warm starts knocking loud at idle and quiets down around 1000 rpm. Called Dealer and they said it will get louder as it is breaking in. I have 3000 on it and it has not stopped knocking after warning up. Will be taking back to dealership this week. I heard others and they don't make this knocking at idle. Very concerned with this issue! Hopefully we can find the problem and have it resolved quickly. Do not want to live this knock. One reason bought this truck was because how quiet the engine was.
 

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Are you guys hearing a knock like metal on metal or an exhaust lope type of sound? When at idle mine sounds a little like it has a lope tune. Mine is the only l5p I've heard so I don't know if my sound is normal or not. My lml didn't have it. I didn't figure it was an issue.
 

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Mine doesn't sound like metal on metal but more like an exhaust type thump or some type of pump noise. Reminds me of the old gas 350 engines that had an air pump installed as part of the pollution crap they installed back in the 70s. The pump would make a similar thumping sound that increased with the rpms. Need to find a way to record the sound. There are a lot of posts on utube if you google "duramax noises" but I couldn't find an exact match to mine.
 

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I purchased a 2020 2500 Silverado a couple of weeks ago, and had this same issue. Dealer had 72 hour or 300 mile or less return policy, so I took it back and got another one. This truck ended up with the same thumping noise. I was told it was normal, but I have also had several duramax diesels, and none of them made this noise. It sucks you pay the kind of money you do for these trucks, and no-one has the same answer. I have it set up to take to other dealership. I will keep everyone posted of what they find.
 

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I have noticed the noise. The more you accelerate the greater the cracking or clicking noise. I tried downloading the video here but no options for it. Any idea on what it could be?
 

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I purchased a 2020 2500 Silverado a couple of weeks ago, and had this same issue. Dealer had 72 hour or 300 mile or less return policy, so I took it back and got another one. This truck ended up with the same thumping noise. I was told it was normal, but I have also had several duramax diesels, and none of them made this noise. It sucks you pay the kind of money you do for these trucks, and no-one has the same answer. I have it set up to take to other dealership. I will keep everyone posted of what they find.
Any updates?
 

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You should not run Amsoil till engine is broken in like 10,000 miles
 

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Any news on the thumping sound from GM or a dealer fix? Mine definitely has it. Not too loud really but the best description I’ve heard yet is that it sounds like the engine is loping.
 

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I'm assuming it's a Duramax? What kind of oil are you running in your truck?
I now have almost 40k on the truck and no knock. I have used Amsoil Signature Series 5-40 since about 500 miles. Change when the friendly computer tells me to or a little sooner.
 

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Hey Guys this is interesting to me although I am not an owner of a 2020 but possibly in the market someday soon for a new/ used. What do these trucks have in place of a Vacuum pump. I have no idea. I work on my own truck so i am clueless on these but interested. Ignorant at best. Thanks
 

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Amazingly there is absolutely no vacuum system in these trucks at all that I can see. We've got hydroboost brakes, and servo motors for air blend doors as far as I can tell.
One of the things I love about the duramax is not having any vacuum stuff under the hood.
 
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