A: my rear differential makes noise (kinda like a clang or?

thanks alot for the help

Mechanic Q: my rear differential makes noise (kinda like a clang or?

my rear differential makes noise (kinda like a clang or ping)... i figured it is the rear differ because when at the back bumper and the truck is rock back and forth the noise can be heard. Also when looking from underneath it almost looks like there is too much play in the differential because you can see the shaft turning and when it stops the noise can be heard.....???? what is this and what do i do?