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Discussion Starter · #1 ·
I bought a new 2020 GMC 3500 HD Sierra Denali in April of this year. I currently have around 4000 miles on the truck. As the weather has gotten colder, I've noticed a rattle coming from the passenger side of the truck. I'm not sure if it's coming from inside or outside the truck. The tone of the noise sounds just like if the jack or jack handle under the back seat is rattling. I've eliminated that possibility by removing them. The noise only happens when the temperature is cold. As the truck warms up, the noise goes away. I drove it all summer and didn't hear the noise until the mornings began to get below 40 degrees. I've had it into both the local GMC dealer and the local Chevy dealer. No one can seem to isolate the noise. The GMC service center didn't do much except just drive it around and verify the noise. The Chevy service center took apart the passenger side of the dash. Neither ended up finding or fixing the problem. The GMC service technician created a GM TAC case which apparently escalates it up to the engineering level.

So far they've eliminated : Passenger side seat-belt; jack/jack handle; front suspension; passenger seat; wiring and stuff under the dash behind the two glove compartments.

This post is a long shot because I don't have anything else to share. One thing I'm thinking of trying is removing the running boards and checking for loose bolts, etc because I think they are Dealer installed. Due to the weather, I'm not excited about crawling around on the ground trying to solve this myself.

Does anyone have any words of wisdom? Thanks in advance.
 

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I am experiencing a very similar issue. Started to hear it this fall when it was getting colder. Usually occurs at high idle when cold or when at low rpms and accelerating from stop. It is a vibration noise coming from the passenger side of the truck. It is noticeable both inside and outside of the cab. It can be felt through the exhaust pipe and actually vibrated enough to fall out of the farthest rear exhaust holder bracket. I put it back on and took it to the dealership for its first service and they add it it to the other list of issue that I have been experiencing. They had it for 2 days and said that they have no clue and if and when it falls off again to bring it in. Dealer service is becoming useless and it is very aggravating.
 

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Discussion Starter · #4 ·
HD Farmer: My experience is a little different because mine only occurs when it's cold and going over a bump where the truck body/frame flexes a little. Specifically when the passenger/front wheel goes down into a dip or bump to cause the uneven stresses on whatever is making the noise. I'm almost 100% convinced it's a metal-on-metal noise. If I go over a bump that causes both wheels to go up or down at the same time, it does not cause the noise. My first thought was that it had something to do with the suspension system...shock, springs, steering, etc. The focus now is under the dash. I'm not sure but I think it's outside rather than inside the truck. I was warned about buying a "first" model year because there were a number of changes made to the engine, body, frame, etc. As an example...I don't know if your engine has a faint "thump" when it idles. My 2013 was a smooth as silk. I'm told they broke the serpentine belt into two belts due to a higher capacity pump or fan that helps keep the engine cool....but I digress from your issue. I have a lot of faith in GM products. I know their engineering, manufacturing process and QA program is very good.

I'm not seeing your problem in my truck but it sounds like you've narrowly defined the problem. I'm surprised they can't put their finger on the problem. Please keep me informed and I'll do the same. No telling what may come from these issues but it can only help to post them and follow up with solutions.
 

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Check how tightly the doors close on the striker. I recently had to 'adjust' both driver side doors to fit tighter against the striker. I had a pretty pronounced thump over bumps that felt like it was under my feet. A few hard smacks with a large hammer to bring the striker in for both left side doors and it's completely gone.
 

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Discussion Starter · #6 ·
Check how tightly the doors close on the striker. I recently had to 'adjust' both driver side doors to fit tighter against the striker. I had a pretty pronounced thump over bumps that felt like it was under my feet. A few hard smacks with a large hammer to bring the striker in for both left side doors and it's completely gone.
I'll check that. I probably won't try to fix myself if it sounds loose. I hadn't thought about the doors. Thanks!
 

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Here's what I found...2020 Sierra SLT HD , mine was the running board mount bracket. It only happened under 40 degrees and then only until it warmed up. Removed boards and...you guessed it, it went away. The dealer and I are looking for after market boards that mount to frame instead of body.
 

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Great news....the boards, believe it or not, have a sequential torque sequence...wow, running boards. 18 ft lbs in a sequence. That stopped the metal to metal sound. Mine was drivers side. Couldn't tell if it was A pillar, door, firewall or something in the fender well. Boards.
 

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Discussion Starter · #10 · (Edited)
Here's what I found...2020 Sierra SLT HD , mine was the running board mount bracket. It only happened under 40 degrees and then only until it warmed up. Removed boards and...you guessed it, it went away. The dealer and I are looking for after market boards that mount to frame instead of body.
Mitch, I wondered about that. I had running boards on a Ford Explorer back in the 90s that did the same thing...my last Ford. My first thought with my 2020 GMC was the running boards. I thought it was due to the fact they were dealer installed options. Usmarine2001 said they looked like they were factory installed based on pictures I sent him. I'll provide this info to the dealership trying to resolve this today. Only thing that confuses me is your statement about "finding after market boards that mount to frame instead of body". I'm not positive but I think the factory boards mount to the frame via threaded holes and bolts. Maybe usmarine2001 can validate my statement.
 

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I still dont have my truck back from dealership (non warranty issue they drove it into something while oil change tire rotation) so I cant run out and look.

18 lbs seems low to me but could be correct...will check later when I get to work. I do know that it is has a smart gun... so my first thought is that the torque would have been correct or it would have flagged the system
 

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Mitch, I wondered about that. I had running boards on a Ford Explorer back in the 90s that did the same thing...my last Ford. My first thought with my 2020 GMC was the running boards. I thought it was due to the fact they were dealer installed options. Usmarine2001 said they looked like they were factory installed based on pictures I sent him. I'll provide this info to the dealership trying to resolve this today. Only thing that confuses me is your statement about "finding after market boards that mount to frame instead of body". I'm not positive but I think the factory boards mount to the frame via threaded holes and bolts. Maybe usmarine2001 can validate my statement.
No, the new body style mounts to body (rocker panels). They torque to 18ft lbs in a sequential order.
 

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Discussion Starter · #13 ·
Do you know what the sequence order is? I’m having the dealer take them off as we speak. Usmarine2001 thinks it’s front to back and to reattach with new bolts.


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Discussion Starter · #14 ·
Well...my latest update isn't good news. They removed the running board and the rattle is still there. I guess Occam's Razor doesn't apply here (The simplest solution is usually the right solution)!

However, the service guy told me the technician found a loose body mount in the front/passenger side of the cab. That could be good news if it can get here quick enough. It may not come in time to do the repair before I leave for Arizona for the winter. Then when I get back, it'll be warm enough that I won't hear the rattle and know if the repair worked or not...until October...again. Frustrating!!

I'm assuming that's the same mount that was flagged and repaired in the factory....according to a contact at the factory. The service technician here said they were told by the TAC engineer overlooking the repair to order a new one from the factory...but it's on back-order...figures! I'm not sure that sounds right to me but I'm beginning to think I don't know much when it comes to the manufacturing process of a truck. I was under the impression the body mount is a single bolt that screws into a weld nut on the frame...instead of a mechanism/part that has to be ordered and installed. I'll continue to wait and see and provide updates to this forum as they happen.
 

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The weld nut is normally on/in the body (all welding is done in body) the body mount itself has rubber on top with 2 studs that go thru the frame... 2 nuts to tighten down. In the center is a hole... a big washer and bolt then go thru the body mount to cab or box .....
 

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Discussion Starter · #16 · (Edited)
UPDATE: Well, the rattle appears to have been fixed! Thanks to "usmarine2001" who injected himself into my problem and worked with my service manager to execute the right solution. He can correct me if I'm wrong but the problem ended up being the front/passenger side body mount. It was either loose or improperly torqued fasteners/bolts on the mount. The fix was to loosen all three fasteners and re-torque. I'm 95% convinced the problem is fixed. I drove the truck down roads that would normally produce the rattle and I hear nothing! Thank you all.
 

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Discussion Starter · #17 ·
UPDATE: Well, the rattle appears to have been fixed! Thanks to "usmarine2001" who injected himself into my problem and worked with my service manager to execute the right solution. He can correct me if I'm wrong but the problem ended up being the front/passenger side body mount. It was either loose or improperly torqued fasteners/bolts on the mount. The fix was to loosen all three fasteners and re-torque. I'm 95% convinced the problem is fixed. I drove the truck down roads that would normally produce the rattle and I hear nothing! Thank you all.
UPDATE TO UPDATE: It’s been several months and about 3,000 miles since my last update. Been on pretty rough roads between Idaho, Tucson and southern Utah. Still no rattle. It seems to be permanently fixed. Thanks again!


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Check how tightly the doors close on the striker. I recently had to 'adjust' both driver side doors to fit tighter against the striker. I had a pretty pronounced thump over bumps that felt like it was under my feet. A few hard smacks with a large hammer to bring the striker in for both left side doors and it's completely gone.

Replying to an old post. How did you tell that the doors were not being closed tight enough?
 
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