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Thought the waterpump was gear driven off cam?
 

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It is, still. But the new big ar$e fan got it's own belt with the upgrade.
 

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We keep seeing this reply on multiple sites (posted by you ) that suggests that GM has this issue managed, perhaps you could convince GM to provide a solution to this obvious defect.
 

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that gm bulletin was from mid-February. For my new 2020 Duramax, the relevant bulletin is the one dated early March and addresses the auxiliary belt thumping as possible cause.
My goal on these duramax forums was to aggregate and centralize information, and another (very intelligent) user on one of the other forums and I pm'ed a bunch of info that led to the state of things today.
I am not a mechanic, and I only know the thumping sound at idle that my new truck makes. Other owners might be experiencing the same sound/issue, or they might have a truck with a completely different issue but mistakenly believe that their truck's issue is addressed by these gm bulletins. I do not believe that gm "...has this issue managed..." as you say. I never wrote that, anywhere, and I do not agree with gm that this is "normal".
I'm close to disappearing from these forums now, because the issue on my truck is the issue from the March gm bulletin, and gm has said that there is no repair/fix. Nothing left for me to discover with respect to this thumping sound. Nonetheless, if I can help anyone, they can contact me and I'll be happy to clarify/help/share what I have learned.
Thanks.
 

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Thumping sound heard at idle and increases with RPM as you drive. Can hear it easily when standing outside front or when listening near front wheel wells and from inside the truck. This is my 4th Duramax so I am familiar with all the ticking noise complaints but this is not a tick. Truck had 660 miles when I Left it with dealer and they said it was "EGR valve operation noise, normal coming from EGR system". None of my other trucks had this loud of a thumping sound. No codes and truck runs fine. Anyone else have this same noise?
Thanks,
Jhc
2020 Denali
2017 Denali
2015 Chevy LT
2008 Chevy LT
I
Thumping sound heard at idle and increases with RPM as you drive. Can hear it easily when standing outside front or when listening near front wheel wells and from inside the truck. This is my 4th Duramax so I am familiar with all the ticking noise complaints but this is not a tick. Truck had 660 miles when I Left it with dealer and they said it was "EGR valve operation noise, normal coming from EGR system". None of my other trucks had this loud of a thumping sound. No codes and truck runs fine. Anyone else have this same noise?
Thanks,
Jhc
2020 Denali
2017 Denali
2015 Chevy LT
2008 Chevy LT
I have a 20 Chevy Duramax with the same noise. Dealer and GM both said it was normal and gave me a printout of the old ticking noise. It is definitely not a tick. My brother has the 19 L5P and no thumping.????????🙄🙄🙄
 

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LHN...We ARE the Joneses
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Oil cooler is different....perhaps they're on track with the similar 'tick' oil flow related scenario?

 

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This is the issue with mine. We went thru the simple steps to remove the aux belt temporarily and the thumping at idle disappeared.
I know another owner in Colorado who had this "aux belt" test done by his dealer, and the dealer concluded that on his truck, this is the cause.
 

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This is the issue with mine. We went thru the simple steps to remove the aux belt temporarily and the thumping at idle disappeared.
I know another owner in Colorado who had this "aux belt" test done by his dealer, and the dealer concluded that on his truck, this is the cause.
If I can help you, I will, but for now this is all I know.
 

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just got mine back from the dealer after a week there. They listened thru all point, front and rear, determined it was coming from the rear of the Engine near Transmission area

Ran 2 other 2020's they had to warm up and both made same Thump/Bumping sound very distinct.

I think some people hear a tick and thinks it the same sound when its not. they reported to GM and currently there is no fix, but it is not related to the drive pulleys
 

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This is my post from another forum, thought I’d share it here too:

Count me as another new owner of a thumping 2020 Duramax, with about 650 miles total. Shortly after noticing the thumping at idle, I Googled it and discovered this forum. I listened to recordings posted here and they sound identical to mine. I was was relieved to learn that GM claims there’s no short or long term effects on engine, disappointed there’s no fix yet to eliminate the thumping.

Tonight after warming up the engine I did the belt removal check and sure enough, the thumping sound disappeared. Reinstalled the belt and the sound returned. Belt looks good and has no discernible seams, lumps or other defects. Pulleys look good too, and the grooves are clean. Tensioner and fan clutch don’t feel abnormal. The tensioner has a smaller pulley so I would think the frequency of the noise would be higher than it is if it was the culprit, and the thump does seem to occur once per engine revolution. So I don’t think it’s coming from the tensioner pulley.

I did notice there is wiring going to the fan clutch, probably to lock it up when extra cooling is needed. What if whatever controls that is sending a pulse to it every revolution? I’m curious whether pulling that plug would eliminate the noise. Has anyone already tried this? Post up if you do try it please. If no one else tries this by tomorrow night then I’ll give it a try.

I’m just brainstorming here and am pretty baffled so far. But I’m determined to figure it out.

So who will solve this puzzle first...GM or us? Please keep us updated if you discover anything new, and thanks for posting this info.

Even with this annoying thump I still love my new truck! It’s a real pleasure to drive and to tow with.
 

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I traded in a 2019 high country 2500 with 4000 miles because of injection problems Tuesday of this week for a 2020 Denali 3500 single rear wheel. Now less that 200 miles I have the thumping sound. State is on lock down now for a month so unless it gets any worse i will drive it till they have a recall.. I love this truck no pedal lag , lots of low in grunt and rides and drives super...
 

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I traded in a 2019 high country 2500 with 4000 miles because of injection problems Tuesday of this week for a 2020 Denali 3500 single rear wheel. Now less that 200 miles I have the thumping sound. State is on lock down now for a month so unless it gets any worse i will drive it till they have a recall.. I love this truck no pedal lag , lots of low in grunt and rides and drives super...
it will get worse, I have seen no issues except the sound is annoying, drive the truck. Hopefully they do find a fix but im not overly worried about it
 

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Thumping sound

Just bought a 2020 3500 with a Duramax Thump thump thump from under the wheel wells and when I opened the hood it sounds like its up top on the drivers side. frustrating to say the least!
Yes, it is a frustrating thumping sound, anyone who is not familiar with the 2020 L5P Duramax will swear it is a main bearing knock !!
 

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My 2020 Sierra 2500 Duramax has the same problem that you are describing. I noticed it just after taking delivery and brought it to the Dealership’s attention, they checked other 2020’s on the lot and advised that at least one other made the same thumping noise. At 7900 km the noise had escalated from a thumping to a definite knocking which now could be heard not only at an idle but also at higher rpm. Currently my new truck is in the shop where the Dealership is making adjustments to the valves. It’s been there for over a week I am hoping to get it back next week I will let you know if they are able to fix the problem. I should also add that this is definitely not the ticking sound that my previous Duramax’s made, I have put 900,000 km on GM Duramax equipped trucks and have never heard this sound. Sure would like to hear if anyone has figured out what is causing this noise.
There is no way that is a valve, rocker arm, lifter noise. The only time that I heard a similar sound was my 68 GTO when it spun a rod bearing. It is not a rod because the noise would increase while increasing and decreasing RPM from idle. Mine sounds to me like a single stage air compressor running in the back ground in time with the engine RPM. It is driving me nuts but I am skeered to death to have some Ace mechanic tearing things apart on a hope or a maybe or just a simple I duh no!!! It is a more than good chance that the result will be a permanent screw up that, if your lucky, toasts the entire mill before the warranty is over!!!
 

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This is my post from another forum, thought I’d share it here too:

Count me as another new owner of a thumping 2020 Duramax, with about 650 miles total. Shortly after noticing the thumping at idle, I Googled it and discovered this forum. I listened to recordings posted here and they sound identical to mine. I was was relieved to learn that GM claims there’s no short or long term effects on engine, disappointed there’s no fix yet to eliminate the thumping.

Tonight after warming up the engine I did the belt removal check and sure enough, the thumping sound disappeared. Reinstalled the belt and the sound returned. Belt looks good and has no discernible seams, lumps or other defects. Pulleys look good too, and the grooves are clean. Tensioner and fan clutch don’t feel abnormal. The tensioner has a smaller pulley so I would think the frequency of the noise would be higher than it is if it was the culprit, and the thump does seem to occur once per engine revolution. So I don’t think it’s coming from the tensioner pulley.

I did notice there is wiring going to the fan clutch, probably to lock it up when extra cooling is needed. What if whatever controls that is sending a pulse to it every revolution? I’m curious whether pulling that plug would eliminate the noise. Has anyone already tried this? Post up if you do try it please. If no one else tries this by tomorrow night then I’ll give it a try.

I’m just brainstorming here and am pretty baffled so far. But I’m determined to figure it out.

So who will solve this puzzle first...GM or us? Please keep us updated if you discover anything new, and thanks for posting this info.

Even with this annoying thump I still love my new truck! It’s a real pleasure to drive and to tow with.
I haven't inspected the belts etc. in fact I haven't even lifted the hood. It sounds to me that you have an objective and correct approach to the Dx. Did you note the water pump or power steering pump involvement? Come to think of it, I once had a power steering pump go dry and cook,, it made a similar sound!! Who knows for sure and how could you isolate these fixtures short of having an arm load of different size belts to bypass various structures!! My hat is off to you for digging into your brand new truck, I'm sure that you will be much more careful than your typical by the hour GM mechanic.
 
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