Worn trans or diff parts. If it gets worse, have it looked at.
Have the engine and trans mounts checked.
i would make sure that the engine is idling at the right rpm cause to fast of rpm can cause that for sure
bad synco rings
sounds like a motor or transmission mount is your likely problem
YOU WILL FEEL A CLUNK WHEN THE VEHICLE IS PLACED IIN REVERSE OR DRIVE AND IS ACCELERATED WITH THE BRAKES DEPRESSED
They could squeak, rattle, bang , clunk.....
You're a clunk-head...
A bad universal joint is one possibility.
when you change directions from forward to reverse it makes a clunk sound and there is a slit delay in movement.
it could possible be the U-Joint which is a cheap and easy fix. it's connected to your drive shaft.
Pull the rear wheels off and check the brakes. Something may have broken or fell apart.
The first thing that comes to mind if the "clunk" is only on starting is worn or broken motor mounts. Something is moving and allowing things to hit each other. A clunking that is intermittent while running may be a ball or roller bearinng going bad.