Vitara - gearbox woes.....

[Apm83]

Arvo all,
My beloved hunting rig started playing up over the weekend.
When 4wd its badly crunching when going into reverse, almost like the previous gear has not disengaged properly...... but this does not happen when in 2wd..

Any ideas on what would be causing this?
Hoping just clutch wear.....

cheers
@