Noise when in Auto or 4W high

[2018TahoeRST]

I have a four wheel drive 2018 Tahoe with the 6.2L. I often drive in "auto" and yes I know that is not recommended. Maybe my tires are shit but if I don't my ass end slides on left hand turns. Anyway I get a loud humming (whirling) noise when I am in "auto" or 4 wheel when I hit the gas. When I take my foot off the accelerator the sound stops. The car has 70k miles and has never made this noise before. I take it to the dealer and the guy just goes "well put it in 2 wheel - problem solved". I slide all over the place in 2 wheel and even the steering seems looser (if that's a word). I figured I would turn to the forums as you guys always seem to know about issues like this. Has anyone experienced anything like this before?

 

[Blackcar]

I'm sure you have bought new tires at some time and if you have, they do anything to change in the way vehicle drives in 2WD. I don't have as many miles on mine and still have same tires which aren't great in stability, but they are getting worn.

 

[Patten]

Mine used to have a whirring sound caused by a loose fit of the front axle and going into the t case. Parts were worn. Seems that is coming back around too even after a t case rebuild.

 

[B-train]

All my vehicles that had the AUTO selection over the years made a little more noise when selected. You're activating the front axle and relying on a clutch in the t-case to engage the front axle when slippage is noticed from the rear wheels. You're going to have more noise, there are more parts moving.

There is one caveat though: if your tires are not a matched set and/or worn like you do burnouts with the rear and the fronts are new, you can end up with driveline binding issues. It will be very noticeable on hard surfaces, not noticeable on slippery ones. 2 sets of tires fighting each other will result in more driveline noise.

Also, I agree with not using AUTO all the time. Just ends up giving you less mpg and more internal wear. That being said, I would highly recommend changing the t-case and front dif fluid if you haven't already.

 

[lbenson]

I've been told driving in Auto on dry pavement will slowly destroy the 4WD system. I always avoid it and only use Auto in snow, and Auto 4WD is only to be used at 55mph and less (been told by GM Mechanics). Not sure why you're sliding all over the place in 2WD - could be the tires on the truck. I never have traction issues in 2WD with Michelin Defenders, not even in rain.

 

[B-train]

Maybe his right foot is made of lead.....LOL. I drive a 2017 with the 6.2L and it will DEFINITELY get squirrelly when the GO pedal is tromped on. However, the stabilitrac keeps the fun to a minimum for sure.......even when I turn it off. Almost impossible to get sideways with it on.

 

[sealandsky]

Hi - I'd start with new tires. I'm running Michelin Premier LTX and have zero issues with the truck getting loose unless I try (and I usually drive with the traction control off). Additionally, my Yukon has the Callaway 560 HP option. It sounds to me that the "auto" clutches are getting worn out and there could be a new transfer case in your future.

 

[RLC2020]

Running in 4wd is not a fix for having crappy tires. There is ZERO reason to drive in 4wd or auto 4wd on dry pavement. Get new tires or stop flooring it in turns. My truck is only ever in 4wd at the boat ramp or when I am off road and actually need it. You're burning up your driveline for zero reason.

 

[shekmark]

Is the four wheel drive system different in an 18 . All the ones I’ve had from GM, while in four Auto, they are two wheel drive and the front only activates if slip is detected. It was perfectly fine to drive in “ ato” all the time. Four high is a different story and you would not use that except in loose or very slippery conditions.

 

[mb1500]

Is the four wheel drive system different in an 18 . All the ones I’ve had from GM, while in four Auto, they are two wheel drive and the front only activates if slip is detected. It was perfectly fine to drive in “ ato” all the time. Four high is a different story and you would not use that except in loose or very slippery conditions.

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

 

[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.