Noise when in Auto or 4W high

[shekmark]

You are correct. The front axle is engaged and the TC clutch is minimally engaged during AUTO. Will have some additional wear driving around in auto all the time but is within the parameters the system was designed for.

If OP has been letting the 6.2 eat in auto for 70k than he might need to have the TC looked at maybe some new fluid:

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163252-9999.pdf

Good link. So in 4 auto, there is still some clutch involvement even though it says it is in 2 wheel drive until slip is detected. Sounds like it is best to leave in 2 wh drive unless raining or slippery.

 

[Fless]

You are correct. The front axle is engaged and the TC clutch is minimally engaged during AUTO. Will have some additional wear driving around in auto all the time but is within the parameters the system was designed for.

If OP has been letting the 6.2 eat in auto for 70k than he might need to have the TC looked at maybe some new fluid:

https://static.nhtsa.gov/odi/tsbs/2019/MC-10163252-9999.pdf

So you're saying that the later models' AUTO setting works differently than the NBS or NNBS? Because on those the front axle actuator doesn't engage the diff until the ATCM senses slippage in the rear wheels. Until then the front diff is NOT engaged. In a normally-operating system the short time lag to engage is noticeable, around 1 second or so.

Would be curious to know if this system is set up differently than the older rigs.

 

[Doubeleive]

sounds like you just have a noisy front diff, used replacements are around $650, could be hit n miss as to whether you end up with another noisy one or not.

 

[mb1500]

It is my understanding that the general function of the system has always been the same, correct me if I’m wrong.

Auto is selected, front (open) diff is electronically actuated and the front half of the drivetrain is being “pushed” by the front wheels. This movement meets the rear axle driveshaft speed inside the auto transfer case clutch system with let’s say maybe 1%-5% clutch engagement. Most cases not enough to cause any sort of binding or issues between the two axles and the driver can operate like this on dry pavement if desired, with only normal wear and tear on the engaged parts vs 2wd. If the computer system senses slippage it will send up to 50% torque up front via the auto tc clutch encoder motor. Engaging 4HI and the auto tc locks in at 50/50 like a traditional system, only to be used on dirt, mud, snow, etc. same with 4LO.

 

[B-train]

You are correct. Auto makes the front diff ready in a coasting state and uses clutches in the transfer case to lock in the front driveshaft when slippage is sensed

 

[Doubeleive]

nothing wrong with using "auto" if there was it would say so in the owners manual, like it does for 4wd
it actually takes some load off the rear diff, and yes there is inherently slightly less mpg, just like there is with AWD like in the Denali or Escalade
is there is additional wear? perhaps a smidge sure, but the parts are spinning regardless of what is used. It's not as if the front differential or axles are not spinning if only 2wd is engaged.
I sure would like to see some proof that you are going to damage anything using "auto" I am willing to bet no one has any....

 

[George B]

To the issue the OP has with noise.
Does the noise you hear change with speed? I also suspect the front differential may be making the noise. I went through a very similar issue with my 2013 suburban at about 70k miles. My front differential backlash was out of adjustment.