Why is there a noise when shifting gears in an automatic transmission?

[JayceLee]

Automatic transmission shifting noise may be caused by the following reasons: 1. Lubrication: The release bearing lacks lubricant, resulting in dry friction or bearing damage. 2. Clearance: There is no gap between the release bearing and the inner end of the release lever. 3. Release bearing: Severe oil contamination or dust accumulation between the release bearing sleeve and the guide tube, or fatigue, breakage, or detachment of the release bearing return spring and pedal return spring, causing poor return of the release bearing. 4. Looseness: Excessive clearance between the driven plate spline hole and its spline shaft. 5. Spring: Annealing, fatigue, or breakage of the driven plate damping spring. 6. Rivets: Loose rivets on the driven plate friction disc or exposed rivet heads.