2.0 auto diff into iS?

[eko]

Noticed in the last few days a whining from the back of my iS.Its only faint at the moment but its bound to get worse.

Thing is im doing the Haynes trackday soon so would rather sort it before then!

So assuming its the diff thats noisy,can i fit the one from my 320i automatic?

I realise it will be longer geard but is it going to be that noticable?

Any help would be good