That brake acts on the rear driveshaft. It could therefore still be an indication that the rear differential is the issue -- the brake shoes could be damping the vibration that's causing the noise.
You should only be using the CDL when you disconnect the driveshafts. For one thing, you shouldn't drive on high-friction surfaces with it engaged; for another, it probably won't tell you anything about your problem.

 

Thanks - a lot of people seem to suggest that test to isolate the problem.

Ok thanks - at least I am getting closer to the source of the problem (I think )

 

No they're not. They are suggesting that you use the CDL when you have removed each driveshaft.

 

Yep, that is what I meant / understood from the messages