There are many potential causes of a clunking noise coming from a transmission, and it can be difficult to diagnose the exact cause without hearing the noise firsthand or taking the vehicle to a qualified mechanic. Some common causes of transmission-related clunking noises include:
1. Loose or damaged engine mounts: If your car's engine mounts are loose or damaged, it can cause the engine to shift excessively, which in turn puts additional stress on the transmission and can cause a clunking noise.
2. Worn gears: Over time, gears in the transmission can wear down, causing them to slip when shifting. This slipping can create a knocking or clunking sound as the gears try to engage.
3. Damaged torque converter: The torque converter is what allows your car's engine to idle while the transmission is in gear (i.e., when you're stopped at a red light). If this component is damaged, it can cause grinding or shaking sensations that may be accompanied by a clunking noise.