My transfer case bevel gear bearing was the fault on my XC90 angle drive, see this youtube video for details...
http://youtu.be/4Af-4DhZ5p8
Needless to say I needed a replacement transfer case which I sourced from a breakers for £324 (with VAT and delivery) and the car is quiet and smooth again.
The transmission had been making a chirping noise between 35 - 45 mph which was the bearing failing, this lasted 9 months before it finally failed.