It may be the free wheel hubs. They do click a bit when working properly and
sometimes make a crunching noise on full lock when cold, but if one
disengages while the other remains engaged than you could have trouble. They
also tend to be more noisy when cold. Try engaging four wheel drive for
maybe half a mile then shifting from four wheel drive to two and then
reversing some distance to disengage in the normal way.
Also there is some kind of maintenance schedule for the hubs, not that
anyone bothers, which you could try.
By the way, AFAIK all Terrano 11 have the 2.7 litre engine [unless it has
the later 3.0 direct injection] but they all have part time 4x4 with
freewheeling hubs.

Huw

I am not a technical person by any means, but I had this in my last
Terrano, and I seem to remember that it is caused by a joint behind
the road wheel which has a plastic washer (just like the cartilage in
your knee).  If this washer wears or gets damaged, you get metal to
metal contact

Sorry if this is a bit vague, but I am working from memory

Callum

I get the same thing in my N reg 2.7TD Maverick when I 3-point turn it
on the drive before a journey, always have done. I try not to worry
about it :-)