[WillAZ]

I have a 2007 BMW 335xi manual transmission. I recently replaced the front driveshaft, the U joint was really loose, and the front right axle because of a clunk I would hear on slow speed tight turns. I took it for a drive after the axle replacement and did a spirited rolling start takeoff and I heard a pop and high speed whine, immediately got off the throttle, drove a little and tried again to accelerate much less spirited and still heard the whining noise. I drained the front diff and transfer case and got pretty clean oil from the front diff no metal, and somewhat dirty oil from the transfer case (I just replaced the oil less than a couple hundred miles ago), but no metal. I was thinking front diff since that is what a lot of posts indicate, but now I'm wondering if its the transfer case not engaging the drive shaft fully? Any ideas?

[ramp]

Just reading through the posts. My e91 manual has developed a whine if going 40mph and let off the gas. Differential, transfer case, just had fluid changed 4 months ago. Hmmm

[Brian86]

Check to see if your halfshaft is still fully engaged in the diff.

There are several reports of a specific aftermarket halfshaft where the C-clip spring between the spline and the diff fails to hold the axle in place.

[E92William]

I had a piece of junk Autozone cv axle in the front that would not stay in no matter what. You can clearly have a look down the exhaust side of the engine and see if I came off. It made a bad rattle noise

[ramp]

Well I took it to a local Euro shop. They said the front differential was making the noise. Checked oil, full, but smelled burnt. They also noted oil pan leak. Quote $2500.00

This is for a 2011 e91 with 6 speed manual. Can't tell from realOEM if the front diff is different for a manual wagon or sedan. Debating with myself if I should do or consider having it done.

[Cm452]

If it whines on the gas AND changes tone, but still whines while coasting the ring and pinion have likely gotten out of alignment and/or worn.
I just went through hell and back with the same problem. No diff shop would touch the thing, and those that said they'd take a crack at it quoted over $800. All of them said it would never be quiet again unless I replaced the worn gears. They said once they whine (not howl, mind you) they quickly "wear in" and cannot be made quiet for prayer or money.
A howl on the other hand, or a "moan" is likely the bearings, which is good news aside from the PITA of getting to the diff.
You drive a manual--the differentials for those are 3-6x the price of the auto ones. Be wary of legendary 3.08 ratio(what you need)--lots of scammers out there trying to sell you an auto diff. RealOEM is your friend. PM me if you need additional help. This process blows.
Good luck!
-Cm

[E92William]

If that was the case I would just pick up both differentials from an automatic xi and have it both be a repair and upgrade. Front diff is tedious to do I bet but rear one is easy so it wouldn't add too much more time to the job and you save money on the manual awd parts.

[Cm452]

I should have been more constructive in my answer, sorry.
First thing's first ; use process of elimination before parts throwing.
A thorough inspection underneath the car and testing the axles or other components for play is a good start. If you heard a pop something broke or came loose. It is best to assess whether it was the latter, and, if the former, whether it can be externally identified.
Sometimes wheel bearings make weird noises when they're toast. Jack the car up and spin each wheel by hand with your other hand on the strut while you do so. If a bearing is bad you will feel a weird vibration in the strut and/or coil spring.
Next, remove the front driveshaft and go for a drive. My whine went away for a while with the front shaft removed but came back 10k miles later as whine under acceleration and coasting. It sounded like a car with square cut reverse gears with the shaft in btw.
A final trick is to put the car up on a lift or high on jack stands and listen to the diff in gear with a mechanics stethoscope. If you do it on Jack stands keep in mind anything snagged by the driveline will pull you in; you'll die a horrific and painful death so don't mess around.
Your clunk and borked shaft may have toasted the transfer case output bearing, and the input/carrier bearing on the diff.
-Cm