Noise from gearbox when applying foot/rear brake

[gluaisrothar]

I was hoping someone out there could cast some light on a noise I wasn't expecting.
Ok here's the scenario - bike is in motion, in 1st gear, clutch is disengaged and back brake applied firmly. Picture an emergency stop of sorts.
The question is, why are there audible clunks from the gearbox. Is this normal/by design?
I really don't think it's ABS - This happens on a R1200GSA LC-2015 & K1600GT-2014 (both wet clutch)

Thanks.

 

[Pukmeister]

The clutch (at the front of the engine) is not connecting the gears to the engine, so no drive, but the gears are happily still doing their own thing inside the gearbox.

The output side of the gearbox is still rotating in time with the rear wheel until you come to rest, so you have first gear still in mesh allowing the gears to rotate and whir/cause noise. Once you come to a stop, the drag from the wet clutch may cause the gears to move within their allowable clearances/endfloat and rattle a little, plus the clutch pushrod will open the clutch plates, allowing clutch plate rattle that can be heard and felt through the drive train.

 

[gluaisrothar]

The clutch (at the front of the engine) is not connecting the gears to the engine, so no drive, but the gears are happily still doing their own thing inside the gearbox.

The output side of the gearbox is still rotating in time with the rear wheel until you come to rest, so you have first gear still in mesh allowing the gears to rotate and whir/cause noise. Once you come to a stop, the drag from the wet clutch may cause the gears to move within their allowable clearances/endfloat and rattle a little, plus the clutch pushrod will open the clutch plates, allowing clutch plate rattle that can be heard and felt through the drive train.

Thanks Adam, that makes sense. As the noise was present on two different bikes, I didn't think it was due to a fault but couldn't work out why. You've explained it perfectly clearly for me.
Thanks again!