Gear Whine
 

Is anyone else getting a really annoying gear whine from their vehicle at roughly 50MPH? It's not outrageously loud but, it is a very distinct sound and once you've heard it you are very aware of it. Even with the radio at a moderate volume. My car is a '10 3.0 with under 2000 miles on it.

I'm just curious if it's a common issue, are there any service campaigns open on it, is BMW just going to tell me it's normal or they can't repeat it and to piss off, etc...

I found this thread:
http://www.xoutpost.com/bmw-sav-foru...onths-e70.html

It's pretty much the only thing that comes up as a result of a search for "gear whine".

I was going to suggest the possibility of it being tire noise... I've rarely come across actual gear whine at the dealer on any BMW. I'd go to the front tires and run your hand across the thread in multiple directions. It should be smooth, but if it feels choppy in one direction it is most likely noisy tires you're hearing.

Which tires do you have and how many miles on them?

I'm pretty confident it's not tire noise. It changes pitch when you are on or off the gas to maintain a constant speed. They are the OEM bridgestones and have less than 2K miles on them.

So the pitch of the noise changes directly with engine speed, and not with road speed? That is important to know to help you diagnosis this.

If it does change with engine speed, I would be looking to eliminate the possibility of it being an alternator whine first (ground loop)

I'm pretty confident it's a gear whine. It's not directly related to engine speed. It is related to road speed. Even if I down shift a gear the sound still happens at 50MPH.

The pitch of the sound does change in relation to the driveline being loaded under accel or decel like a gear whine. I'm guessing its got to be coming from one of the diffs. If it were the trans it would probably change with gear unless it were on the output shaft side of things.

NEW DEVELOPMENT! :D

We just got an E70 in the shop that had a pinched seal at the front differential... it was leaking gear oil while driving at a rate that would have it empty within a few thousand miles. Luckily for this customer we noticed it when it was in the shop for something else. From the looks of it the seal is easy to be damaged during installation, even at the factory as this one only had a couple thousand miles... The seal in question is an o-ring on the axle output where it slips into the oil pan.

#8 in this diagram.
RealOEM.com BMW E70 X5 3.0si Final drive (front axle), parts, 4-wheel

If this happens to be pinched during installation thus leaking it could very well be the front diff you are hearing and you would get a new one under warranty. I'd book an appointment with the dealer ASAP and schedule for a loaner car if you need one as it will take a few days to a week in the shop if this is the case.

Good to know. I'll roll up under there and see if I can find any evidence of oil leaking.

You'd need to look right where the front diff meets the oil pan with the plastic underpanel removed. It would have a stream/trail aiming straight down from the gear oil.

Also was just reminded by another thread that it could be wheel bearings as well... don't know why that one slipped my mind as one of the possibilities.