this is roughly how i would go to rule out what the problem is NOT.
If the noise is there with the clutch pedal is down and up its a good bet its the clutch or thrust bearing
if it is only there when the clutch pedal is down then it is a problem with the clutch or thrust bearing.
if it is only there when the clutch pedal is up then it is in the gearbox.
if it is there in neutral it is likely to be the input shaft bearing,
if it is loud in the lower gears and quieter in the higher one it could be countershaft bearings.
if the noise is a rattle and only happens when you engage the clutch its probably the clutch.
serisouly the cheapest thing to do is put redline shockproof oil in the box, think bout it
oil $180
clutch $300 and up if you do it yourself
gearbox $1000 +
even if you do put the redline oil in and the noise is still there you can just drain it and reuse it once you have fixed the problem, its not like it will do 20000km before if the problem is still there.