1 Inspect DIFFERENTIAL BEARING Worn or dry differential bearing.
2 Inspect DIFFERENTIAL CAPACITY Low differential fluid level
3 Inspect DIFFERENTIAL FLUID TYPE Improper differential fluid level or differential fluid type.
4 Inspect DRIVESHAFT CENTER SUPPORT Loose, worn or damaged driveshaft (center support) carrier bearing.
5 Inspect CLUTCH BEARING Worn or improperly alligned clutch bearing.
6 Inspect DRIVESHAFT Damaged, loose, or improperly balanced driveshaft.
7 Inspect MUFFLER Restricted, loose or burned out muffler.
9 Inspect TRANSMISSION BEARING Damaged or worn input shaft, countershaft, or drive gear bearings.
10 Inspect U-JOINT Loose, worn or damaged u-joint.
or if its a different sound try this link
http://autozone.com/servlet/UiBroker...arameters=info