clicking sound on a citroen c5 gear box?

hi room
i have a citroen c5 2.0l petrol 2002 52 thousand miles on the clock, and was wondering if anyone has had any problems with the gearbox on this model.
there is a clicking sound which seems to be coming from the gearbox, some days its louder than others.
i had the drive shafts looked at and was given the all clear on them.
the noise only happens as im driving.
thanks again for all your help.

james
June 2009