Auto 4wd noise?

zz2h33 · January 27, 2019

Checking in here with the same issue 2014 Silvy 6.2L. Audible humming noise with AUTO or 4H engaged under acceleration and goes away while coasting. It is quite loud even my passengers have asked if something was wrong. I bought the truck with 40k miles now have 75k and have always had the noise. And no I don’t drive in auto 24/7, just use it occasionally for what it’s intended for. Seemed to get worse after putting taller tires on and leveling kit. I rented a 2018 Silvy a few months back and tried it in Auto just to see and it was quiet with zero noise. So i’ve been worried and basically waiting for something to majorly break until I ran across this thread where it sounds like it’s fairly common. My questions are: 1) could this be related to final gear ratios in our trucks experiencing this? I have the max towing package and since adding taller tires it has definitely compounded the noise. 2) have any of us experiencing this noise actually had anything break such as not engaging auto or 4wd and the service 4wd message? 3) have any of us experiencing this noise been able to pinpoint it and have it fixed?

diyer2 · January 27, 2019

Have you changed the fluids in the diffs and transfer case?

They all make noise, hum.

Taller tires puts more of a strain on the drive line IMO.

sk · January 28, 2019

I didn't read back through this whole thread but there is a TSB for the whining noise. It tells the Techs to put some insulation on the module under the dash. Sorry I don't have a link to the thread but if you search on this forum you should be able to find it.

TwoBallScrewBall · January 29, 2019

As has been said a dozen times in this thread already:

4HI and Auto both LOCK the transfer case in 4WD.

The front axle has an electronic clutch pack that remains locked in 4HI, and only engages when wheel slip is detected in Auto.

The "4WD" gear noise is normal to hear in both 4HI, 4LO and Auto, since the transfer case is locked and spinning the front driveshaft in all 3 modes.

Had a 2016 and now a 2018 and they both do the same thing. Dealer also confirmed this when I had to take the 2016 in for the recall for the transfer case controller, which left me stuck in full time 4WD HI after accidentally driving in auto for an extended period of time on a camping trip.

Also, as was also stated, do NOT leave the truck in auto all the time. It is terrible for the transfer case. You're basically causing unnecessary wear if you have it engaged in dry conditions.

Plenty of people will continue to chime in saying they've never had an issue and drive in auto all the time. Great for them. It's a matter of if, not when, you will have a problem. Why leave the transfer case engaged when 95% of the time you don't need it???

zz2h33 · January 30, 2019

Screwball not sure if your post was directed at me or not but I wasn’t asking for a lesson on how the 4wd/auto system works in these trucks. I know very well how they work and I know how it’s been stated multiple times in this thread because people like to repeat things to try and sound smart. I also stated very clearly that I DO NOT drive in auto. I’ve own two GMT900 trucks and a 360 (trailblazer) all with the same system and none of them had this noise in addition to the K2 I rented for a while did not have it. What I hear in this truck is ABNORMAL compared to my experience with these trucks and that’s what really has been stated MULTIPLE TIMES in this thread and this is what the thread is really about. So thanks for stating the obvious, again, for those that don’t know what is actually spinning when in auto or full 4WD ...but it’s absolutely no help.

ftwhite · January 30, 2019

Not only that, but its just wrong info too. If you want to know how the 2014-2018 transfer cases work, go read about them. Magna Powertrain MP3023/3024 if you have RPO code NQH. The manufacture clearly states how Auto mode works. There is no normal griding noise, at least not defined by the manufacturer. But any fix is expensive. I'd suggest getting a "second opinion" from an independant transmission or differential shop, and using that to pressure the dealer if you still have a powertrain warranty. the lift should only be a problem if the drivetrain angles were not taken care of, but it will be an easy excuse.

BTW, I drive 80% of the time in Auto. I only really use 2x when on the highway in summer to save a little gas. 3rd truck, pervious 2 over 100k, and no TC "wore out" yet. But everything wares out at some point I guess.

Lawman86 · September 24, 2021

On 2/8/2015 at 7:34 PM, pancepance said:

Yes, I get a noise during the switch from one position to another. My concern is a constant mechanical gear/gear type noise. Similar to a rear end as its starting to go. This noise will increase/decrease with speed and is only apparent out of 2wd.

I rode in a '14 Silverado today that had no noticeable noise when operating in auto or 4hi. Compared to mine its a night and day difference.
I also noticed today that when in auto if I come to a complete stop and reverse there is a clunk as a start in the other direction. Then if I stop and go the opposite direction it clunks again. Similar to the sound a bad U-joint can make when starting from a standstill. This is new and I hadn't noticed prior but it does it consistently each time. Just one time from standing start at regular pace. Not any type of power takeoff, just as if you were making a 3-point turn in a parking lot. Each time I change direction there's a clunk and then not again till I've come to a complete stop and restart motion.

Same here today. I was backing up a hill in auto and mine did the clunking sound. Haven’t had it do it before in 4 lo or 4 hi. Just noticed it today, but I was on a very steep incline(it was a one lane logging road and someone was coming up as I was going down), and when I stopped I put it in neutral and then shifted to auto and it started the clunk noise. I said the hell with it and just put it back in 2wd.

BigBadSierra · September 24, 2021

14 hours ago, Lawman86 said:

Same here today. I was backing up a hill in auto and mine did the clunking sound. Haven’t had it do it before in 4 lo or 4 hi. Just noticed it today, but I was on a very steep incline(it was a one lane logging road and someone was coming up as I was going down), and when I stopped I put it in neutral and then shifted to auto and it started the clunk noise. I said the hell with it and just put it back in 2wd.

Don't get confused between 4Auto and 4 hi and lo. 4Auto uses slip clutches to function so they will never bind up. 4 hi and 4 low can always bind up an click given the right conditions. I only use 4 hi and low if I'm on a surface that can slide the tires if not it's auto.

Lawman86 · October 18, 2021

On 9/24/2021 at 12:37 PM, BigBadSierra said:

Don't get confused between 4Auto and 4 hi and lo. 4Auto uses slip clutches to function so they will never bind up. 4 hi and 4 low can always bind up an click given the right conditions. I only use 4 hi and low if I'm on a surface that can slide the tires if not it's auto.

That’s what I thought. I tried it on Hi and Low and it did just fine

ftwhite · October 23, 2021

Everything that is spinning in 2wd, is also spinning in 4wd (auto, 4h, 4l). The only difference is how it all connects together. Variable clutch pack in transfer case for 4auto and locked clutch in 4h/4l.

So if the sound goes away in 2wd, and only happens in 4auto, then I would suspect something in the transfer case clutch pack. Could be noise caused by lift changes (angles usually) that only gets exposed by torque. So still the transfer case clutch pack not working right, but exposed by lift.

I bet a good transmission/diff shop can give you a much more educated opinion on if it is something you need to fix, or just let be. I wouldn't trust a dealer's opinion only.