A noisy 5-speed manual transmission in neutral could likely be caused by?

A noisy 5-speed manual transmission in neutral is typically not caused by issues with the bearings mentioned in the options, particularly when considering the transmission is not engaged in gear. In neutral, the input shaft is allowed to spin freely, and while the bearings can produce noise under load or during gear engagement, they would not typically make noise when the vehicle is in neutral and stationary.

Therefore, if the transmission is making noise only when in neutral, it might indicate a different issue unrelated to these bearings, such as issues with the gear synchronizers, noise from other components, or even external factors like vibrations from the engine or drivetrain components. Understanding that in the neutral position, the transmission has less rotating mass directly affecting the noise can help clarify why a bearing issue is unlikely in this scenario.