Usually, one thinks the transmission which it could be. Sometimes though it can be the rear differential because of the gear reduction you have in reverse versus in a forward gear. If there is play in the rear differential that is when you will hear it. U joints can also do that. Some of the guys on here have had issues with the rear driveshaft splines as well.
I only hear if if I open door
Then it is normal, no problem.
I removed my catalytic converter and muffler, I can't hear the clunk anymore.
I ignored a noise recently too. Then my transmission went on holiday…. Try to address it for peace of mind.
Ive already replaced transmission once before
If you can't hear it in the cab with the doors closed, it is most likely normal. Any vehicle makes noises in normal operation, and it is not logical to take it to the dealer for every noise that is heard, unless it is an abnormal or very loud noise. The clunk going from forward to reverse is normal in any car on the road, an exception may be an EV having direct drive.
