To understand a clunk during a gear change, compare it under normal, safe conditions: cold versus warm, idle versus steady speed, and light versus higher load. Record the gear change, road speed, throttle, and whether the engine is cold or warm. Change one condition at a time so the result stays useful.
Do not create a risky test just to reproduce it. Check for warning lights and recent drivetrain work; do not repeatedly provoke a hard shift.
Quick educational note
For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.