I had the same problem in my sunny wagon.
Sounds like it could either be your uni joints in the tailshaft are worn and knackered or theres to much play in the diff...
Pity the uni's arent replaceable in these tailshafts so they need to be drilled out. Best thing to do would to inspect all parts to see if their out of factory specs

Does it happen on deacceleration also? And if your coasting (no foot on the gas) does it make this sound also?

Dave