Growling noise on deceleration -- UPDATE

[jdstrickland]

In gear (D), or out (N), my X5 makes a growling noise that I think is coming from the front diff, or the t-case -- can't tell which one. This is a new noise that started on Saturday evening. I pulled the left front tire to check the brakes in preparation for a road trip, and then drove the car and it was fine. The Mrs. took it to San Diego, and says the noise began on the way home.

The symptom is that the noise is not there when driving, it is only there when coasting. Shifting into N does not change the pitch or volume. I don't think the CV joints are involved, else the noise would be there when turning, and is a different noise anyhow.

I have to drive to the airport on Wed, and plan my road trip on Sunday. I'm not sure where to begin looking for the source of the noise.

I could drop the drive shaft, this would eliminate or confirm that the noise is from the t-case, what other tests can I do?

++++++++++++++++++

Pinion Shaft Bearing was the problem.

Under load the shaft moves one way and the thrust on the bearing is minimal, if any. On deceleration, the weight of the vehicle pushes the shaft into the thrust bearing and the loading on the bearing is very high. When the bearing is worn (I am not sure how or why this happens) the noise it generates is loud. When I first heard it, we were on an errand that took 2-ish miles to complete so we forged on. The mechanic is less than 10 miles, so about 20 miles round trip on surface streets. 10 more miles back for service to be done, so about 35 miles from when I first heard the noise to when I left the car for service. The noise changed in that time, and became worse.

So, if your X5 starts making a noise from the front end when you let off of the gas, you have about 50 miles, depending on how fast you are going and how often you let off the gas, before the pinion bearing gives up completely. You mileage may vary, but you are not going to be driving for long.

RealOEM.com does not list internal parts to the front diff, although I see no reason why a transmission supply would not carry this part. I wish I was not constrained by time and a schedule that was set in stone, else I think I could have fixed this. The mechanic charged 8 hours.