Gearbox noises

This sounds very much like a shift fork rattle. More than likely the rattle that you are hearing is the shift fork vibration against the synchronizer.

These shift forks are supposed to have pads on them that will dampen the noise and vibration but these get worn down and they start rattling.

Unfortunately the only way to know if take it apart. However, if you get the rattle to start, press the shifter into a gear as if you were going to engage a gear but don't push hard enough to put it into the gear. Basically just hold the pressure on the shifter which will pull the shift fork against the gear and it may make it stop. If this does then the shift fork is the issue.

Let me know if you have questions or this doesn't make sense. Thanks