In a manual transmission, a grinding noise is heard when the vehicle is in neutral and idling, but the noise disappears when the clutch pedal is pressed. What is the most likely worn component?

• A. Worn pilot bearing
• B. Worn input shaft bearing
• C. Worn clutch release (throwout) bearing
• D. Worn auxiliary transmission countershaft bearing

Answer: (B)

A grinding noise that shows up with the engine idling in neutral and goes away when you press the clutch points to a fault on the input shaft that is loaded when the engine is connected to the transmission. The input shaft bearing supports the end of the shaft as it turns with the engine. If that bearing is worn, you’ll hear grinding while the input shaft is spinning, which happens when the clutch is up. Pressing the clutch decouples the engine from the transmission, so the input shaft stops turning and the grinding disappears. The release bearing would typically cause noise when the clutch is operated, not just idle, and a pilot bearing or countershaft bearing would produce different noise patterns not matching this exact clutch-disengaged behavior.