As I have upgraded to an XE fairmont ghia with a 351 cleavo in it I had to do a few things for a roadworthy. The main one was getting the gas tank recomplianced. when i put it in i took it up the servo to fill with gas without the seats in. What i am getting is a whining noise. Thw transmission changes fine and the diff does not clunk when going into gear.
Its a consistant whining - thinking its an axle bearing. But i have been told they are not common to make noise. Is this correct?

What do i have to exaclty do to figure out if it is the bearings or the diff?

(Even in netruel it makes the whining noise)