Yep the classic gearbox getrag rattle
Also due to the thin viscosity, and small amount of oil used in these boxes that gets thrown up to the higher parts of the box. RPM also dictates how noisy they can be too. Mine with A/C on will be noisier, and if it is warmed up at idle revs.
Add 10 or more years of use, plus getting rid of the factory dual mass flywheel and they are a pretty noisy box as bearings slowly wear and clearances also open up.
Sometimes if I want it to be just a little quieter, I can just tap the clutch when waiting at the lights in neutral and it will be a bit quieter. I think this is due to the input shaft getting into a dead central position (talking in thousanths of an inch) and making less lash noise in general.
Some people recommend changing the input shaft bearing, or recoing box, but it really is just the way the box is as time goes on as well as using non OEM flywheels.
There are some that are noisier than others too.