GarrettSR5,

The pinion sounds like a fairly low level "rushing", "roaring" or almost like a semi-periodic wind noise but happens at all road speeds, and varies with road speed. Seems to come from the transmission tunnel and also seems to be transmitted through the shift cables to some degree. Independent of engine speed (rpm) or if the clutch is in or out. Clutch actuation changes the sound slightly, as does the current gear selection, since those things change the load on the pinion bearing. I think I've heard that 4th gear places the highest load on the bearing for some reason, and it does seem louder but it's hard to tell. Also in full load or full engine braking is surprisingly quieter (for me at least), feathering the throttle in gear, clutch engaged, so that the load through the drivetrain is close to neutral stress (coasting) seems to make the most sound.

Hope that helps, it's hard to describe in words.