My CTD has come down with what sounds like a bearing howl. it also could be mistaken for tire road noise. The symptoms below are when operated in 2WD. I've not had the chance to check it out in 4WD yet.

At about 20mph a low pitched growl becomes noticeable. It increases in pitch and volume until about 45mph where it is more of a howl than a growl. Then it seems to begin to get lost in the increased vehicle noise (including a more obvious turbo whine) that goes with the increase in speed.

Going from full power to coasting seems to have no effect on the noise. This is why I considered tire noise at first. Plus, it sounds a lot like tire road noise.

When I kick the transmission out of gear into neutral, after the transmission finally disengages the growl/howl subsides and goes away. When the transmission is reengaged it resumes again.

I'm beginning to suspect the transfer case and possibly it's output shaft. Any suggestions or other possible sources for the noise?

TIA for any help or advice on this one.

 

From the symptoms I would agree with you that it is in the trans or transfer case. Rearend pinion bearing would change noise when going from power to coast but output bearing on trans would still be loaded. I would drain trans fluid and see if there are any obvious suspended metallic particles, although I doubt that you would be able to see anything unless something has already grenaded.

Better yet, put it up on a lift and run the rpm up in gear with somebody listening to the trans through a pipe or mechanic's stethoscope. Easier to locate the source of the noise that way. Just be careful when under the lift - make sure it is capable of holding a vibrating truck.

Let us know what you find. I can always stand to add to my mental catalog of symptoms and fixes thereof.

 

Your trans and t/case ideas sound right. There is a large ball bearing inside the overdrive housing of the automatic which I have seen fail several times. Go for a drive and when the trans has shifted into fourth, push the button to force a 4-3 shift. If the noise changes a lot when you do this, that may be the cause. A stethoscope will help to confirm it.

 

Thx guys. I finally got the time to check it out a bit further yesterday. I put it up on jackstands to get all 4 corners off the ground. Then, started it, put it into gear and crawled under it to listen. It's the transmission. I'm sure it's coming from in front of the transfercase.

Now, for the noise to be as constant as it is, it has to be from the back portion, behind the where the gears are changed. Could it possibly be the pump or something similar? I would think if it was from the output shaft there would be some change in the noise in reaction to loading and unloading it.

I love my CTD, but I've never had a vehicle that has cost so much to keep it runnin'. Reminds me of some women I've known.

EDIT: I've just run the onboard diagnostic. I get a fault code 45. This indicates an open or short circuit in the Transmission O/D Solenoid Circuit. Could this be related to the noise?