grinding noise under the truck
 

Hi friends I drive a chevy silverado 1500 Z71 2003 4WD:metal:
and i have this noise under the cab first guess tranfer case (hole in case) nop
I put some welding JB and works no Leaks since two years I remove the front shaft and no more noise my question Guilty orden still #1 tranfer case#2front diferencial and #3 front drive shaft any clue? I dont want to remove tranfer case yet and found the diferencial or shaft where the problem how to test each?:waah::waah::waah: