Weird whirring sound in 4wd auto

Mikedfw · March 29, 2020

So when vehicle is in 4wd auto, whenever accelerating there is a strange kind of mechanical whirring/whistling noise, it disappears a soon as I stop accelerating. It does not make this noise in 2wd.

Was told that it was normal for being in 4wd auto and basically I shouldnt be driving in that mode for any extended period of time. I was in it because of bad weather, and it was my understanding it would be more like another vehicles awd system.

Has anyone heard this noise in this mode? It definitely doesn't sound normal to me. And what is the point of auto mode if you aren't supposed to use it any differently from 4wd high? I was told manual said not to leave it in auto, but it only says that about 4wd high.

fishlessam · March 29, 2020

Will try mine to see if i can detect any noise.

Mikedfw · March 29, 2020

16 minutes ago, fishlessam said:

Will try mine to see if i can detect any noise.

Thanks

Silverado4x4 · March 29, 2020

26 minutes ago, Mikedfw said:

So when vehicle is in 4wd auto, whenever accelerating there is a strange kind of mechanical whirring/whistling noise, it disappears a soon as I stop accelerating. It does not make this noise in 2wd.

Was told that it was normal for being in 4wd auto and basically I shouldnt be driving in that mode for any extended period of time. I was in it because of bad weather, and it was my understanding it would be more like another vehicles awd system.

Has anyone heard this noise in this mode? It definitely doesn't sound normal to me. And what is the point of auto mode if you aren't supposed to use it any differently from 4wd high? I was told manual said not to leave it in auto, but it only says that about 4wd high.

When you shift to auto 4 wheel drive, your front axle is engaged so all of the components of your front axle are turning as you drive (front shafts, driveshaft ETC). The transfer case DOES apply a very slight (maybe 5%) rotational force (torque) through an internal clutch to the front driveshaft and because the front axle is engaged, it is ready and waiting for a "slipping event" from the rear axle. When the vehicle senses a difference in speed from the rear axle to the front (rear wheel slip), the clutch within the transfer case applies MORE torque to the front driveshaft to make the front and rear axle turn at the same speed. Kinda like a slightly slipping 4 wheel drive. If the vehicle continues to see a speed differential from the front and the rear axles, the clutch within the transfer case continues to add more torque and eventually will be locked in. As the wheel slip goes away, the transfer case returns to the 5% mode and waits for the next slip event. When you put the vehicle in 4 HI, the front axle is engaged and it receives 100% torque through the internal clutch within the transfer case. Never drive in 4H on dry roads and make turns this will bind the driveline, straight line your fine but never in turns. 4auto you can leave it in auto all the time if you want but really there is no need but maybe burn a little more fuel. I might use mine in on and off conditions where I don't have to keep shifting to 4H and back to 2H.

Edited March 29, 2020 by Silverado4x4

Mikedfw · March 29, 2020

The noise I'm hearing only occurs while pressing on the gas pedal, even mild acceleration, it doesn't matter road conditions. I know it does it even if it isn't engaging the front wheels, that is why I'm confused about it.

If it happened all the time or only when there was wheel slippage, I'd chalk it up to being normal for the mode, but it is only in acceleration, even if extremely mild acceleration on road conditions that wont cause slippage.

I drive in 2wd about 99% of the time, just want to make sure the other modes are working properly for the occassions I do actually need them.

DogMom · March 29, 2020

So when vehicle is in 4wd auto, whenever accelerating there is a strange kind of mechanical whirring/whistling noise, it disappears a soon as I stop accelerating. It does not make this noise in 2wd.

Was told that it was normal for being in 4wd auto and basically I shouldnt be driving in that mode for any extended period of time. I was in it because of bad weather, and it was my understanding it would be more like another vehicles awd system.

Has anyone heard this noise in this mode? It definitely doesn't sound normal to me. And what is the point of auto mode if you aren't supposed to use it any differently from 4wd high? I was told manual said not to leave it in auto, but it only says that about 4wd high.

I have the whining whistling noise while in 4WD High

Sent from my SM-G965U using Tapatalk

Jvdubsx2 · October 28, 2020

I have the same noise and conditions on my 2015 Silverado and GM thought I was crazy when I brought it in.

204Denali · October 28, 2020

On 3/29/2020 at 1:01 PM, Mikedfw said:

So when vehicle is in 4wd auto, whenever accelerating there is a strange kind of mechanical whirring/whistling noise, it disappears a soon as I stop accelerating. It does not make this noise in 2wd.

Was told that it was normal for being in 4wd auto and basically I shouldnt be driving in that mode for any extended period of time. I was in it because of bad weather, and it was my understanding it would be more like another vehicles awd system.

Has anyone heard this noise in this mode? It definitely doesn't sound normal to me. And what is the point of auto mode if you aren't supposed to use it any differently from 4wd high? I was told manual said not to leave it in auto, but it only says that about 4wd high.

LOL this is the same question I asked just yesterday and I was getting roasted for asking it.

What you are describing is exactly what I experienced for the first time other day. Switched into 4wd due to snow and every time I accelerated it made the noise your describing for a short period of time and then go away, and like you said only during acceleration.

Everything else seemed normal and no issues I could see.

Glad I'm not losing my mind. I knew someone would have experienced what I'm talking about, rather than non-help I received on my post

diyer2 · October 28, 2020

204 Denali

Not busting your balls. Your post was hard to understand IMO. MIkes was not.

The noise is normal. Look at a parts diagram. Lots of parts including a chain to make noise.

Edited October 28, 2020 by diyer2

newdude · October 28, 2020

Normal. The interiors are quieter on these as well as the last gen. Some more noise makes it through the cabin from the transfer case and the front diff.

Auto is fine to use on say wet pavement or some snow, 4 HI you might want for an un-plowed road.

204Denali · October 28, 2020

1 hour ago, diyer2 said:

204 Denali

Not busting your balls. Your post was hard to understand IMO. MIkes was not.

The noise is normal. Look at a parts diagram. Lots of parts including a chain to make noise.

I got the answer I was looking for, I don't take it personal, just glad I now know