Transfer case whining?

[dross99_si]

Hey guys,
2007 Tahoe LT 4WD we have a very faint whining noise when rolling. Almost like an old police siren. Only happens when cold like for the first few miles. This morning I drove with windows down, got it up to 30mph and shifted to neutral. Volume/pitch of the whine is totally dependent on vehicle speed not RPM. Came to a stop and changed selector to 4WD high and drove for about 1/4 mile. Sound definitely changed. Also got the service 4WD system message after changing selector. Put it back in 2WD. After a little more driving through the neighborhood the noise went away. No clunks or any other symptoms. No leaks either. I changed the fluid myself 20k miles ago. This is something new that just started a few days ago.
Unless it's something other than the T-case...
Have any of you experienced something similar?

 

[thompsoj22]

The tc will not "warm up" in a few miles? give the u joints a good inspection. try warming the vehicle in the driveway to operating temp before driving and see if it still does it, the tc does have a planetary and chain both of which could make some noise if worn but i dont think the noise would go away. ill guess a dry u joint?Or possibly a front wheel bearing? The warming in the driveway will rule out "temp related" as opposed to driveline rotation.

 

[wjburken]

I’m not sure what letting the vehicle run in the drive way will do as far as ruling out a transfer case issue that seems to go away after it warms up as the Transfer case won’t be turning.

The fact that there is a Service 4WD message on the dash tells me that something is a miss with the Transfer case. Not sure if wheel bearings to u-joints would contribute to that message showing up. Not saying that the u-joints or wheel bearings can’t be bad also, but from what @dross99_si explained, I would spend some time checking out the transfer case. Might have a transfer case motor going out and not fully engaging or disengaging.

Do you typically keep the vehicle in 2WD or in Auto4WD? Do you have the ability to read any codes that might be present due to the Service 4WD message?

 

[thompsoj22]

I’m not sure what letting the vehicle run in the drive way will do as far as ruling out a transfer case issue that seems to go away after it warms up as the Transfer case won’t be turning.

The fact that there is a Service 4WD message on the dash tells me that something is a miss with the Transfer case. Not sure if wheel bearings to u-joints would contribute to that message showing up. Not saying that the u-joints or wheel bearings can’t be bad also, but from what @dross99_si explained, I would spend some time checking out the transfer case. Might have a transfer case motor going out and not fully engaging or disengaging.

Do you typically keep the vehicle in 2WD or in Auto4WD? Do you have the ability to read any codes that might be present due to the Service 4WD message?

I was thinking it would rule out transmission noise IE, pump, converter, trans planetary? letting the trans get to op temp and driving with the windows down to determine if the sound is still there for the first few miles. The transfer case is isolated from the warm up, troubleshooting online is truly just guessing based upon the op description of the problem. Your right, i did not pay close enough attention to the fact that tc has a code, no guessing required, it is likely the tc.

 

[swathdiver]

...have a very faint whining noise when rolling. Almost like an old police siren. Only happens when cold like for the first few miles. This morning I drove with windows down, got it up to 30mph and shifted to neutral. Volume/pitch of the whine is totally dependent on vehicle speed not RPM. Came to a stop and changed selector to 4WD high and drove for about 1/4 mile. Sound definitely changed. Also got the service 4WD system message after changing selector.

Do you have the ability to read any codes that might be present due to the Service 4WD message?

Andy, let's put the Tech-2 on it. Give me a call.

 

[dross99_si]

Thanks for the replies everyone. The Tahoe was due for front diff fluid and oil change. After I did these the whining noise I posted about has mysteriously gone away. :Shrug:

But, the issue with the transfer case is still present I'm sure. The service 4WD message has gone away for the moment. We usually keep it in 2WD. I just selected 4WD that day to see if that whining noise changed.

 

[Fless]

The Service 4WD message could be one of many things, but most likely electrical. Dash switches lose communication with the TC control module, body grounds or other connectors get corroded, etc. It's a good practice to exercise the 4WD system from time to time, too. Getting the code using a Tech 2 or similar should help narrow it down; even though the Service 4WD indicator isn't on, there could be a stored code to see.

 

[swathdiver]

The Service 4WD message could be one of many things, but most likely electrical. Dash switches lose communication with the TC control module, body grounds or other connectors get corroded, etc. It's a good practice to exercise the 4WD system from time to time, too. Getting the code using a Tech 2 or similar should help narrow it down; even though the Service 4WD indicator isn't on, there could be a stored code to see.

Andy's got access to one any time he needs it.

We make it a point to run ours through the paces at least once a month.

Also think putting the transfer case in neutral would be a good theft deterrent, along with some wheel chocks!

 

[dross99_si]

So this whining siren noise was gone for a while, but does come back from time to time only if it's cold outside and once the vehicle has been driven for a while and everything is warmed up it goes away. Could it be the tires perhaps?

 

[dross99_si]

Ok so let's start over on this.
Forget all about the transfer case and 4WD aspect that I previously mentioned.
The whining/siren noise is still occurring at speeds greater than 20mph. Only makes the noise when cold. After the vehicle is driven for a while the noise goes away.
Perhaps it is a u joint. How do I service this properly?