[Ian]

***ASSUMING IT IS A REAR NOISE***

drive at whatever speed it is that the noise happens at and swerve left and right. if it gets louder when you swerve left, its coming from the right (right side would be receiving most of the weight transfer). if it gets louder when you swerve right, its coming from the left (left side receiving most of the weight transfer).

if the noise stays the same when swerving left and right, you'll have to check the pinion and carrier bearings. jack up the rear and put some jackstands under there to support the car. get a friend to "drive" the car while the rear is up in the air. once you hear the noise, listen with a screwdriver to the front of the center section near the pinion yolk. then listen to either side of the center section just before the axle tubes using the same screwdriver method. if you still can't determine where the noise is coming from, you'll have to open it up and take a look or take it to a shop and have them look into it.