[dougbert]

I have had the car for 4-5 years now, and do my own work. It has been reliable but recently the noise coming from the drivetrain is getting strangely loud. It is not tires. It changes frequency with speed, but does not change when you are on or off throttle, the noise is consistent. It does seem that at speeds closer to 90-100 mph that the noise is less. It could be that it is drowned out by the rest of the car at those speeds. It also does not change in a left or right turn, and checked for wheel bearings. I did change the transfer case fluid, but nothing changed in terms of the noise. I now have it up on jack stands and took the exhaust off to check the driveshaft bearing. It seems OK. It does have a strange metallic click near the transfer case when you move the shaft. See the attached video.

"https://vimeo.com/796080489"

What else could it be?? It is driving me nuts.

[dougbert]

Could it be the transfer case chain is worn or stretched?

[jadams161]

I watched your video. Play (lash) like that is normal as long as the U-joint is not loose or moving. look for rust around U-joint. You definitely need the rear output shaft seal done. Also I would make sure that no wires are exposed where the plastic covering has come off that bundle of wires seen in the video. This is the noise I hear in mine for a few miles when driven cold. It only does it around 30-39 mph.
https://www.youtube.com/shorts/OwMd8sgFzxI

[dougbert]

Thanks for your reply! My TC does not sound as bad as yours in the video. I was wondering about the main driveshaft and I currently have the TC out of the car. The driveshaft U-joints and hanger bearing seem OK.

I pulled a replacement TC from a junkyard but it turned out to be trash. I think it was flood damaged, as the inside was all brown. The front to rear clutch pack was seized, so the wreck may have been caused by shitty handling in wet corners due to no differential action.

It is useful to have the junk one because I took it all apart and put it back together to understand how to do it on my good transfer case. I checked all my TC bearings, and they are good. All the parts look very clean with some magnetic particles stuck to the magnet at the bottom. My thinking is that the oil seals were bad enough to lose a lot of oil in a short amount of time. I did replace the oil once, which seemed to cure the noise problem for a while.

I have all new seals and the proper BMW TC oil and I will be putting it back together this week.

I plan on replacing the differential oil in the front and rear diffs while I have it on jack stands. I love the car as a daily driver, with 178,000 miles on the car.