What kinds of sounds do you get from the transmission when the car is in gear and moving?How about when you step on the clutch while the car is moving, how does the sound change, if it can be heard?
Are there any issues selecting any gears, or is there a particular gear that can be selected that has a significant inpact on sounds from the transmission such as 4th, which should be direct drive?
Lastly has the transmission oil been changed? There is a magnet on the drain plug, inspect it for metalic particles, and watch (collect) some of the oil which could even be sent into a lab for analysis. A very common location for failure without other symptoms initially isn't the input and output bearings, it's the input shaft's mid bearings. The input and output shaft main bearings when they fail usually cause other symptoms more noticeable under different loads.