Rear Differential Grinding

[hownnq]

Question guys. I changed my differential fluid awhile back and did not use the BMW OEM specific fluid and started getting a grinding noise. If I change it back to the OEM fluid will it go away or do I need to get a new differential?

[Jack Dabsy]

That's the 64,000 dollar question my friend... If it is constantly "Whining" then it is shot !!
Maybe a bearing or two in the crown, or drive-shaft bearing(s)...

[brettski]

I have heard of this sort of noise issues from an experienced aftermarket diff mod shop, they always recommend the BMW fluid for all of their clients, and if people use something else, they suggest changing back to the BMW fluid to address the issue. I guess its easier and cheaper to change the fluid and see how you go from there.

[sprintman]

The OEM BMW fluid is nothing special. Just a common Group IV (PAO) basestock fluid with an average aditive package. not something I or anybody I know uses in their BMW. Exactly what fluid id you use when you changed it, which is by the way a very good idea.