1) Noise is dependent on road speed, not engine speed. 2) Noise is present in neutral with enough road speed. 3) Noise is present with clutch depressed and enough road speed.
If the noise is present in neutral with the clutch depressed and enough road speed, the only thing that is rotating is the output shaft. I think the rear main bearing is a good guess.
Yes, along with anything beyond or driven by the tail shaft, such as the speedo pinion and such. The bearing is certainly a suspect, even though the noise doesn't sound like a bearing.
